Thanks for your questions.
Basically, the color-blending mechanism works by converting the RGB colors defined in the theme to HSL colors since HSL color space is used for the calculation of the new colors based on the color you specify as a base color. The base color that you define when initializing the color blending determines a certain range that is used when the color variations are created. This range is calculated so that only near colors to the base color are used (so that when you choose Red as a base color, only colors near to Red are utilized etc.). In this way, the same "color pattern" is preserved, only the Hue (HSL - Hue, Saturation, Lightness) is adjusted so that the new color "feel" is created.
Please note that color blending is only applied to RGB color settings defined in the themes. If you have any images in your theme, they will not be affected by the color-blending procedure.
In our mechanism we have implemented our own routines for RGB to HSL conversion. You can find many techniques to do this on the Internet as well.
I hope this will clarify the main idea of color-blending. You can write anytime if you have more questions.
the Telerik team