As a Roblox developer, it is currently impossible to get the dominant colors from an image/viewport.
For example, if an API was made to get the dominant colors of a picture, it would make it way easier to create UI for certain situations. Here are examples of one use case. (Portrait of a Roblox Character)
Click to expand.
Also, here is an example of a site that gets the dominant colors from a picture. A similar thing could be implemented in Roblox, for example, a function
:GetDominantColors(colorAmount: number) could be added to ViewportFrames and ImageLabels. It would be also great if developers could pass the number of dominant colors they would like to get. (In the image below I have chosen 5 colors to be returned on the site.)