The "selection" color or highlight color can not be set by a theme. It is controlled by a registry setting in the device.

If you are not comfortable editing the registry or don't know how to make a back-up of it do not proceed!
Navigate to
HKLM\System\SysColor. The value found there is a long sequence of hex-values for the various display elements. Each element consists of the Red-Green-Blue color pairs of letters/numbers and a "00" which serves as a separator. For example,
00 00 00 00 = black,
FF FF FF 00 = white. The highlight color is at index 13 (beginning at 0). Change the color at that position by editing the RGB hex values. I think you will have to soft-reset to see the changes.