[BUGFIX] Invalid allowed value for color space

The array with allowed color space names contains an invalid value
(grey), which is replaced by the correct one (gray).

Resolves: #50287
Releases: 6.2, 6.1
Change-Id: I96a2a1c4b55fc32e95a68f0f8ff0304d8de7bc51
Reviewed-on: https://review.typo3.org/23023
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters