it is a pink curve. It is a 3dB/oct curve. Gain is 0dB at niquist, and starts decreasing from there (subtracting 3dB for each octave). It is slighly different from the pink filter created in 2412, because you have there an hardware filter recreted (and a pink med coming from a modified version of the pink filter). It is the same filter used in pink strip channel, hence the gui symbol.