The Right Trim will often match the left trim. A single colour is sometimes used to cover over the Trim Colour and give the 'Header-Footer' design. In this case, the left and right trims will be coloured the same as the 'Body Colour'.
When using a single colour in your trims, a small graphic (75 x 100 pixels) can be used with the 'repeat' option checked.
Keep in mind, the right trim joins with the header at different places, depending on the screen size and resolution. Flexible design is the key to a good scheme.