A few suggestions to create realistic sample’s

• Make the paint test on a moveable and repositionable surface. Something that can be affixed temporarily to any wall, ceiling, or even floor (when you are painting a floor). Note: do not use your blue tape on the edges of this! Tape the back side only..
• Make the colored surfaces in proportion to each other, for example: Trim colors will usually be narrower than the wall color surfaces.
• Be sure the surface you paint the test on is primed, or at least under-painted with a color similar to what you’re testing. For example, you can of course use poster board but since it’s paper, it must be oil-primed so it does not warp. Personally I like the flat-finish, fast drying low odor products for this. Note: I’ve typically prepared up to 20 or so poster boards with this type of oil primer, to have ready to go in advance–and easy to use at a moment’s notice–when preparing color tests for clients.
• Roll on 2 coats of your finish (test) color, making the application as close to what you intend to do on the final surface. Use a roller with similar pile to what you plan to use on the job.
• Use a stable surface with a texture similar to the wall or surface to be painted. IF the target surface is textured, it’s worth it to make a replica since color reacts so differently with the light falling on textured or smooth surfaces.
• Be sure to do the test with the same finish you’ll be using on the actual surface (Flat? Eggshell? Semi-or-high-gloss?)
• Label your sample cards and cut a nice, smooth-edged one about 8”x8” to leave with the client for their own ‘shopping’ purposes.. I find that people appreciate this especially when they are looking at window treatments and furnishings.