I would probably go with the barn/fence paint then, so long as it's an exterior alkyd paint. As a back-up plan, you might try to contact Ace Hardware and ask them what company makes their paints for them. Typically this is done on a contract basis. The manufacturer of the paint would be much more knowledgeable than any one at Ace.
I'm very reluctant to suggest you use the Ace paint because of the reasons explained in the previous posts. I hope you understand and concur.
Now, does this barn / fence paint come in several premixed colours? That is, does it come ready made in a "red", or a "brown", or a "reddish brown"? If so, that's done because they can add more pigment at the factory than they can at the point of sale, so a premixed colour will hide better than one tinted at the paint store.
And I think you should use a traction grit in your paint even if you could buy it in flat. The difference in surface roughness between a flat and a gloss paint is enough to see, but not enough to prevent water planing. You can slip on a wet flat paint almost as easily as a wet gloss paint. But, I've never used a traction grit in any painting I've ever done, so what to use and how to use it is something I can't advise you on. I do know that Sherwin Williams paint stores have a traction grit called "Shark Bite" which you can add to anyone's paint, but whether it's a good traction grit or not, I simply don't know.
PS: You don't need to know the rest. It explains why you can ruin latex paint by adding too much colourant to it. There's a common misconception that you can ruin oil based paints by doing that too, but this is just a misconception. Oil based paints will be slower to dry if heavily tinted, but will still form a normal film in the end.
The reason you can ruin a latex paint by adding too much colourant is because the carrier fluid in the 12 different paint colourants in the paint tinting machine in the paint store is GLYCERINE. Glycerine is used as a carrier fluid for paint tinting colourants because it's soluble in both water and mineral spirits, so the same paint colourants can be used to tint both latex and oil based paints. That means the paint store only needs to have space for one tinting machine, and it can tint all the oil based and latex paint they sell.
The problem arises with latex paints being tinted at the store. Latex paint is essentially a SLURRY of hard clear plastic blobs (called "binder" resins), hard clear or white "extender" pigments that lower the gloss of the paint and coloured particles (called "pigments") (like the white pigment, Titanium Dioxide" that's already present in white tint bases or coloured pigments added when tinting the paint) all suspended in a solution of water and a low volatility (pronounced "slow to evaporate") solvent called a "coalescing agent". Once the latex paint is applied to a wall, the water starts to evaporate, and those clear and hard plastic blobs (the binder resins) find themselves surrounded by the coaleascing solvent at ever increasing concentration. The coalescing solvent softens the clear hard plastic resins so that they're easily deformed (pronounced "squishy"). Then, the same forces of capillary pressure and surface tension that causes tiny water droplets to coalesce into large droplets in a rain clowd work to cause the soft binder resins to pull on and stick to each other to form a continuous soft plastic film with the extender pigments and any coloured pigments suspended inside that film very much like raisins in raisin bread.
Then, over the next day or two, the coalescing agent evaporates from the soft paint film, and that's what gives you that "freshly painted" smell. (If you smell a freshly painted smell, you're smelling the coalescing solvents, and chances are it's a product called "Texanol". I've dabbled with the idea of buying some Texanol to give every one of my apartments that "freshly painted smell" to impress prospective tenants regardless of whether I painted the apartment or not.) And, as the coalescing solvent evaporates, the plastic film (consisting of binder resins) hardens back up again to the same hardness those resins were before the paint was spread on the wall.
Now, what happens if you take a gallon of latex paint and add TOO MUCH colourant in the paint tinting machine. Because the carrier fluid in the colourant is glycerine, which evaporates even slower than the coalescing solvent, as the water evaporates from the paint, the concentration of coalescing solvent won't get as high because of all the glycerine. And, the concentration of coalescing solvent in that glycerine is only going to diminish because the glycerine evaporates slower than the coalescing solvent. The result will be that the plastic binder resins won't soften up as much, and the result is that you may not get proper film formation. The result is likely to be a very low gloss paint job that's pale in colour and that you can rub off the wall with your finger.
The solution to that problem is to add the pigments to the paint to give it colour, without adding any glycerine, and that is exactly what's done at the paint factory when they make a "pretinted" paint (either latex or oil based). Because they can add as much pigment as they want without adding any glycerine, pretinted paints generally hide a lot better because they have more pigments in them than can be added at the point of sale (without ruining the paint).
Now, all of the preceding doesn't apply to oil based paints. Oil based paints have a very robust film formation mechanism that causes the paint to form a proper film come HE11 or high water. If you add so much colourant that would wreck a latex paint to an oil based paint, all that would happen is the paint would take a lot longer to dry while the low volatility glycerine evaporated from the paint. Once it had evaporated, and the alkyd resins were exposed to the oxygen in the air, then the oil based paint would form a film normally as though there hadn't been any problem. It's just a common misconception that you can ALSO ruin an oil based paint by overtinting it. People figure whatever applies to latex paints applies equally well to oil based paints, and vice versa, but that's seldom true.
Still, if you can get a pretinted exterior oil based paint, it will give you better hide than one tinted at the store. That's simply because the tint base you buy at the store will be limited by the amount of empty space in the can provided for adding colourant. At the factory, they can add more dry pigment to the paint, and then fill each can full of that highly pigmented paint. At the paint store, they can only add as much colourant as there is empty space in the can.
If you can get a pretinted exterior alkyd barn or fence paint, I'd jump at that option. If your company doesn't sell a pretinted exterior alkyd, you might want to phone around. It seems to me that a red or reddish brown exterior alkyd barn paint would probably be pretty popular. But, do you want a red or reddish brown porch?
