The Pearl 8100 had the hardware to support multi-color lights in the trackball area. The 8310 does not - it just has a white LED vs the red, green, blue and white ones the Pearl does. You won't find an app that can change the trackball color on the 8310, just the notification LED colors.
You'll have to get a colored trackball, dye your trackball, or cover the white led with some colored tape to change the color.
RedNightHawk is correct,
There are many videos on youtube showing you how to place a piece of colored tape in front of the white LED making the light the LED produces the color of the tape. Someone told me they did that and they got sand in their trackball but their warranty wouldnt cover it due do fiddling with the unit. Its quite a risky operation just to have a colored trackball.
I saw someone take a sharpie and they removed the trackball and colored in the LED light under the ball. This made the ball light up without coloring the ball. It looked cool but haven't tried it yet.