Ideal Color Space

It is practically impossible to find a perfect working color space.

Kodak ProPhoto RGB, Adobe RGB (1998) and sRGB are examples of gray balanced and perceptually uniform RGB working color spaces.

Gray balanced means that equal RGB numbers always produce a neutral gray whereas perceptual uniformity implies that the similar adjustment number produces approximately the same degree of visual change within the working color space.

Large color space may not be ideal, so does small color space
Large color space such as ProPhoto RGB contains huge gamut which cannot be fully visualised on today monitor screen. Any correction done with wide gamut cannot be checked until the actual result is printed out. Every output device too has its own gamut thus added uncertainty and complication to the overall color reproduction. On the other hand, if the working space is significantly smaller than the input device such as camera or scanner, the possible colors in that image would be clipped and permanently loss when converted to an output gamut.

An ideal space would be one that color difference is minimised when converting from one color space to the other or vice versa.