> A-118 white noise sounds dark and filtered. Adjusting "Blue" and
> "Red" on Coloured noise doesn't give true white noise either. I
> wonder, if there is a mod to bypass the filtering

The A-118 derives the white noise simply by amplifying the noise of the
base-emitter transition of an npn transistor. Each transistor generates a
little bit a different noise. Probably your A-118 contains a transistor with
a more dark noise. Replacing the transistor Q1 may change the noise sound.

Best wishes
Dieter Doepfer