You seem to be using Q2A v1.7.4 and a modified SnowFlat theme. The simplest approach would be this:
1. Edit file qa-theme/SnowFlat/qa-styles.css
2. Look for these CSS selectors and change the colors inside (don't change the selector names only the colors!):
.qam-ask-mobile a.turquoise
.qam-search-mobile.turquoise
.qam-search-mobile.turquoise.active