如何在不减慢过程的情况下使用颜色进行文本着色？

I have found that time of the string colouring depends on how many different NSColors are used. In code below if I use only one colour for the three cases then the text colouring process is 3 times faster than in the case when three different colours are used for these three cases, each colour for each case. Why ? Is there a way not to slow down the colouring for three different colours ?I have found that time of the string colouring