I think you are trying to create a gradient color pattern. If so, you need to set the first color and the last one.
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[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.
_______
[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.