If there are no rows with multiple lines, then you should remove the XTF_VARY option. In that case, setting XTR.ITEMLINES =2 should increase the row height by a factor of two. If that's too much, then -1 is probably your best bet (as the height for editable cells is normally somewhat taller than the height for static text). You can experiment with -3 thru -6 but on my high res monitor, I don't really see any difference between them.
As for the header color, no, unfortunately, that is one attribute of XTREE that does not appear to be colorable. The closest you can come to that is to eliminate the header entirely (set XTR.HIDEHEADER = 1) and then create a pseudo-header line (set Advanced Coldef Option HdrLines=1) which you can color using the row coloring mechanism.