How can i know how many source color can be extracted from an image?

[AvocadoCookie]

since the number of possible source colors varies for different images and an excessively large index will cause the following problem:

Error:
   0: Failed to get source color.
   1: Could not get source color from image: ...
   2: Source color index 2 is out of bounds (0-1)

how can i know how many source colors i can choose from in a script to avoid the problem?

[shreudi]

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