Make baseline color more distinguishable

Baseline plot is currently quite confusing. Second baseline and those after
has color irrelevant to the sample it's comparing to. The patch should make
them more distinguishable by setting baseline colour closer to the sample
than its neighbor.


git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@212118 91177308-0d34-0410-b5e6-96231b3b80d8