The good news is that it looks like you have no clogged jets. The bad news is, as you can see, that there has been some cross contamination of black into your cyan and magenta at least. I don't have an XP900, so I don't know its inner workings specifically, but most Epsons have a print-head parking position that puts the heads into a kind of rubber cup that is supposed to prevent air from getting in and drying them out. When there is a lot of loose ink in the printer then this cup can get contaminated with ink. Once it's contaminated it acts as a spot where ink can backflow back into the other colours.
What creates a lot of loose ink? Head cleanings and borderless printing. Head cleaning is obvious - it intentionally pumps ink through. Borderless printing creates excess ink because the printer starts printing slightly before the edge of the page, and that ink has to go somewhere. The head cleaning mechanism generally includes a rubber squeegee and a soaker pad to absorb the ink from head cleanings, but when it's saturated then it leaves ink on the surface of the head, which then gets into that rubber parking cup. There is generally a strip of sponge under the print head track to absorb borderless printing ink, but often some ink gets left on the head and can end up in other places.
What to do: First of all stop all head cleanings and all borderless printing for now. Use LibreOffice Draw or some such program to create a test print page, like what you were doing, but make it blocks of pure Cyan, Magenta, and Yellow only. You need to get the ink that has back-flowed into the head back out and onto paper.
You will likely need to do some cleaning. This requires some judiciousness. You need to get the print head off its parking position - I don't know the firmware of that printer well enough to know exactly how to do that. Most Epsons have a button you can press and hold down for that. Look yours up. Sometimes you need to use a bit of force, but this is where the judiciousness comes in because some heads lock in the parking position and you don't want to break that. You want to get the head off its parking position so you can get in there with cotton swabs and get the excess ink out. Some cleaning fluid will do you well. I make mine with 1/2 cup 95% denatured ethanol, 1/2 cup of glass cleaner, 1tbsp amonia. If you can find the rubber parking cup and cleaning squeegee make sure you clean them until a cotton swab with cleaner doesn't come back with any ink on it.
Sometimes you can get some of the soaked in ink back out of the soaker pads with paper towel and make them absorbant again. There are also videos on how to replace the waste ink pads for that printer. There may be some videos for what I've described above too.