I fear this may be a better question for Stack Overflow since it's going to be pretty much solely programming-related, but I have two theories. First off, Swift is fast, and colouring a string is a linear-time thing, so this should be very very quick. If its slow, you can expect a big bug introducing polynomial complexity. Perhaps:

1) If your colouring involves modifying the string itself to include colour tags, or just for whatever reason does a copy of the string without actually modifying it, that may cause your loop to re-run until nothing is changed. In essence, you run the loop once per coloured character, rather than per change. Test this by seeing if adding 1 letter 10x quicker than pasting in 10 letters at once.

2) If colouring itself is slow, which it shouldnt be but hey, modify the code to start off by finding a difference between the old (coloured) string and the new string, and only try to colour those new indices. All the previous work can then be re-used. But dont go crazy on this approach, since you'll end up implementing diff, and thats a much harder problem than it looks. Instead just try to reuse colouring indices for any shared prefix/suffix only.

Hello vytarasov!

We believe that this post does not fit the main topic of this site.

As has already been pointed out, this is a programming question, not a bioinformatics one, so it's off-topic for the site I'm afraid!

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