What does "interpolate no end color found" mean ?"

[micheus]

I think you are trying to create a gradient color pattern. If so, you need to set the first color and the last one.
_______
[edited]
From that other thread
We set each color key and use Interpolate between them to create the gradient:

Calling Interpolate after the last color key (red) will result in that message you has pointed.