You can switch between a custom pivot and custom roadmap for the same report. Both those reports have different default colour sets when you select the custom colour theme. This can be confusing for a couple reasons.
If you select a custom colour for something like the text, it might be visible against the background on the pivot, but not against the different coloured background on the roadmap.
It is not clear which colours will change between the pivot and roadmap. When you select custom theme, your report will start using the default values. If you switch report types, it will use the other report types default values. The only way to lock down which colours you get is to select the colour from the picker, even if it's the same colour.
For example, in the attached screenshots, I have selected a pink background for the row headers. The default text colour is different for the two roadmaps. I would have to select the row header text and explicitly pick either white or black for them to be consistent.