Re: adding color pigment
First, you don't want to mix different sheens or you'll wind up with something that can't be duplicated later should you need more of it. Preferably the paint would be the same brand as well, but at the very least it should be the same sheen.
If you can't get a paint dealer to give you a few drops of several colorants in your own containers, then contact painting contractors that have the ability to custom mix paint. You may be able to negotiate with them to tint your paint for a small fee.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!