If you do make an agreement like this with your landlord, you should ask him for the brand, line, gloss level and colour of the paint. The reason is that you can buy the same colour and gloss paint for $12 per gallon and $52 per gallon, and the only thing similar between them will be the colourand gloss. That is, they'll look the same, and that might be all he cares about, but it's certainly not the only difference.
Also, if the landlord knows what he's doing, he'll be using a mildew resistant paint in his bathrooms. So, if you want to paint the bathroom, you should get the same information from him regarding the bathroom.
Bathroom paints rely on the ability of the mildewcide within the paint to migrate to the paint's surface under wet or humid conditions. If you paint over a bathroom paint with a different bathroom paint, or a paint that isn't intended for use as a bathroom paint, you could prevent the mildewcide reserve in the old paint from migrating to the new surface. So, it's always best to paint over a bathroom paint with the same brand of bathroom paint to get the benefit of the mildewcide reserve that's still remaining in the old bathroom paint.