I am painting several rooms in my home. I had read somewhere that the bedroom should be a darker color than bathroom in the same section of the house or vice versa. The hallway should it be a darker shade or lighter shade than rooms branching off from it. Or does any of this matter at all. Please shed some light.
Personally I think that the color of paint you choose should be based on your own personal preferences and not necessarily what is recommended. You live in the house and you are the one that sees the paint every day. If you have two rooms that are shared (master bedroom / master bathroom), then possibly painting those rooms coordinating colors would be nice, but to think that one specific room should be darker shouldn't really matter.
It all depends on the lighting in your home. If the rooms get a lot of light then you can make them darker than the hallway. If the room lighting isn't good you want a lighter color so it doesn't look like you're stepping into a dark cave. The hallway should be a medium to lighter color since hallways usually have poor lighting and you don't want them to look too dark. There's no rule I know of for the bathroom, I'd just go with how much light the room gets and darken or lighten the paint as needed.