Where is the problem

I am using wt32-eth01 ws2815. There are 1200 LEDs, while the light turns on properly at the beginning, the colors change towards the end. Is there any affordable controller you can recommend?

I would guess bad connection down by where that issue is or moisture intrusion or not enough power. Did you add any power injection?

If your connections look good and you don’t suspect a bad pixel, then take a look at 1200 pixels on one port. At 40 fps you’re sending new frames before the data gets to the end of the string. About 800 pixels is max at 40 fps. I’d recommend you split the pixels into 2 ports at least, maybe 3 by adding a couple of GPIOs and then running a data wire and connecting down the line. Wasatch Pixels has controllers that are affordable that have level-shifting and power/data outputs if you’re looking for an affordable controller.

way to mutch pixels for that projekt
even with a 3INCH spacing it looks good on a Outdoor frame
no need to add this amount of Nodes