QScintilla - Add color to words in a custom lexer

I am trying to create a custom lexer based off of JavaScript for QScintilla. I have figured out how to add keywords the the lexer. However, I can not figure out how to alter the way they look when typed in like it does when you type the word function.

I need to figure out how to do this with for example the word "fill".

Here's my code:

    api->add("fill");
    api->prepare();
    ui->textEdit->setLexer(lexer);