Highlight on computer-delivered Reading is a find tool, not a study method. Spend seconds on the deciding sentence, then move. If you colour a paragraph, you have used time the next items still need. The paper is still about 60 minutes; highlight does not pause the clock. Do not build a colour system. One mark on the sentence that could answer the item is enough. This page is about timing, not about highlight versus paper underlining, and not about which colour to pick. Practice IELTS is a computer Writing and Reading tool. It is not the official familiarisation test, not a booking page, and not Listening or Speaking.
Take 1 free scored test (Writing or Reading) at https://practice-ielts.com. Then $14.99 for 3 months of Writing + Reading. Not official IELTS.