For the current line highlighting, open src/Sigil/ViewEditors/CodeViewEditor.cpp
, line 864:
QColor lineColor = QColor( Qt::yellow ).lighter( COLOR_FADE_AMOUNT );
to e.g. Qt::black
, this will make the highlight background black.
If you want to disable line highlighting altogether, in the same file, comment out line 866:
selection.format.setBackground( lineColor );
by adding // to the beginning of the line, so that it becomes:
// selection.format.setBackground( lineColor );
then recompile Sigil.
FWIW, if you still have the directory where you previously compiled Sigil intact, just edit that file, then run make again, it'll pick up the changes and recompile only the necessary bits, i.e. you won't have to compile everything from the beginning.
AFAIK, the tooltip colours come from the colour scheme your system is using, so you have to change it there...