Using Colorize effect has unexpectedly high performance penalty on flicking

Colorizing a number of icons (about 16) in a GridView has significant impact on the flicking
performance of the view, even with a very high cacheBuffer value.

As the icons are static and the flickable page is cached, there's no reason the icons should
be redrawn when flicking, so whether the icons are colorized or not should not have any big
impact.