One of the things I just realized was that because it's hard to know when the brush is clean, the colors mix a bit on the brush and look dull. When you use your hand or separate brushes for each colour you could keep it all brighter because the colours are less likely to mix and look dull
Maybe it’s just takes a lot of layers, but I’m inclined to not trust the internet 😭 (sorry for doubting you) It kinda looks like the colors aren’t appearing until after a very convenient cut… (I’m implying that real paint was used in between cuts, but again, I’m not sure if it just took multiple layers to show up well 🤷)