Off topic:How to program the colouring of DNA sequence?

Question

[vytarasov]

I am using Swift for Mac programming and I see that to color all “A”, “T”, “C”, “G” in a long sequence during its editing is quite slow, there is time lag between typing and displaying the colored sequence. I calculate every time new ranges for all “A”, “T”, “C” in the sequence and then loop through the arrays of ranges to add color to “A”, “T”, “C”. How is usually this coloring done in other programming languages which are more often used in bioinformatics ? I guess I am doing it not in effective way in Swift.