(using s2putty s60v3 1.5rc1)
First of all, I must say that I'm really pleased that the alternate colour palettes finally got implemented. Before, I had to keep my E90 running old hackable firmware just so I could access s2putty's private directory and modify the colours in the profile text files directly. I guess I can finally upgrade now, without being forced to install s2putty on memory card instead...
Anyway, when using the grey-on-black palette the "ANSI White Bold" colour (number 15 in PC textmode palette) which should be pure white (255,255,255) is shown exactly the same as "ANSI White" (textmode number 7), ie. 187,187,187 which is light grey. Bolding the default terminal foreground colour, which is also 187,187,187, works ok and results in white as it should.
For example, I'm using irssi with its default theme. The activity indicators on the status bar are colour 15 in the theme (%W), not whatever is the terminal's default fg colour (%N) so they appear as grey when they should appear as white. This can be worked around by modifying the theme to use default fg colour for them instead, but I still think this should be fixed in the palette itself for other apps where you can't really do anything about the way they do terminal colours.
I guess this is simply a remnant from the times when the only palette was the black-on-white one, there it makes sense to force white into grey so you can actually see it on the white background.