Since there are no independent attributes for the ticks, only tailor-made tricks spring to mind.
The result of this
imagesc(abs(peaks(10)));
colormap('bone');
set(gca, 'XTick', 0:pi:2*pi, 'XTickLabel', {'0', 'p', '2p'}, 'fontname','symbol');
a = gca;
b = copyobj(a, gcf)
set(b, 'Xcolor', [1 1 1], 'YColor', [1 1 1], 'XTickLabel', [], 'YTickLabel', [])
is this