Rosebutter, welcome to the Fish Pond. This is the info from the walkthrough --
THE CHEMICALS: Click on any color and watch the paper on the right, it will have a series of symbols on it. Let's suppose you click on the color red and an x comes on the white page then the color red is not the first color of that code. You then click the color green on the page, now a check-mark appears next to the color green. That means that green is the first color, now you need to find the second color. Click on yellow, if an x appears next to the check-mark then yellow is not the second color.
The page will now start on a different line. Click the green first because we have already established that it is the first color. Then click on the color purple, now you have 2 check-marks so you know that green is the first color and purple is the second color. Keep experimenting with colors until you get 4 check-marks. Once that is completed a number will appear on the screen just turn the dial on the lock to match the numbers on the screen