Easiest way is to add ret = 1-ret; to the comp shader, to invert everything. Add it *after* the ret *= GetBlur2(uv); line.
For the colors you should probably change the r,g,b equations for the custom waves and in the preset's per frame code. Use a format like wave_r = 0.5 + 0.5*... this way the value of wave_r will always be between 0 and 1. If you want to tone it down even more do wave_r = 0.5 + 0.3*... this way the value can be no more than 0.8
