The range differs.
new() and fromHSV() allow a range from 0-1.
fromRGB() ranges from 0 to 255.
Also, I do not think you can get the color of a shirt as it is a bitmap image. If you do want to try anyways, I would write an API outside of Roblox do some techno-gizmo stuff where it parses the image and finds the median color range. I wouldn't actually recommend this for any game since it requires a pointless amount of time and resources to make.
An alternative is to simply store color data through a Color3 instance as a child of the shirt. Then read the value of the instance.
If this was not what you meant, just message me.
2 comments
The Color3 is always represented as a matrix having each number between 0 and 1.
but why is it that using Color3.fromRGB allow 0 to 255? Color3 for clothing items are 0 to 255.