[pdftex] Rule color madness

[G. D. Brettschneider]

Well, it's not so important for me, so I didn't check
the archives to see whether or not this has been discussed
before, but I'm a bit surprised by this little file returning
two lines in different colors instead of the same (with
pdfTeX 1.00b):

  \pdfliteral {0 1 1 0 k}% switch color to red (CMYB)
  \hrule height 1pt      % draws black line
  \vskip 1pt
  \hrule height 1.01pt   % draws red line
  \vfill
  \end

So it seems that rules must be thicker than 1pt before they
can be given a color other than black - whereas colored
letters are allowed to have thinner lines. Such behaviour
would not be desirable, however, because TeX's standard
rules have a thickness of only 0.4pt. - I came to this
problem when writing a macro to underline text without
using math mode.

Gerolf

BTW: Is there a more appropiate way to convert CMYB to RGB
than saying: R=1-C, G=1-M, B=1-Y? How to get a "Black" value?
Can pdfTeX do the conversion by itself? - At least, link border
colors can be defined by handling RGB values to \pdfstartlink.