The image of the dinosaur is greyscale. The SVG then uses a, feFlood & feComposite to combine the SourceGraphic with the flood-color using an arithmetic operator. This operator is kind of a lot to get your head around (because MATHS ), but it has 4 additional attributes: k1, k2, k3 & k4 that work like this:

result = k1*in*in2 + k2*in + k3*in2 + k4

In this example, we can ignore k2 - k4 because k1 does everything for us: the results of in * in2 (the dino image and the flood-color) multiplied by the value of k1 - in this instance, 1 . Note that this only works so well because we're using a pure greyscale image as a base - full-colour images can still be colourised, but not in the same way, as the flood-color is multiplied by the original colours in the image itself.

Then we're just using GSAP to loop through an array of colours and append a change of the filter's feFlood flood-color to the timeline. Nice! ✨