Hi, has anyone else noticed that if you enter RGB values manually on a solid colour generator in FCPX it looks off. I did a test, entering the same values in FCPX and Photoshop, and FCPX is definitely different. If I then use the magnifier to "pick-up" the colour I made in Photoshop, it gives a different RGC value than what I entered manually in Photoshop. I know the Photoshop one is the correct one because it visually matches the brand colour I'm trying to match.
RGB values are always dependent on what color space you are using. So the same color should have different values in different color spaces.
I guess your problem is that you are entering the values in the Rec 709 color space (standard for HD movies) without knowing it. This means you get other colors than if you enter the same values in sRGB or Adobe RGB color space, which is the standard in Photoshop, depending on your setup.
(Side note: Standard for display/webb would be sRGB and for print Adobe RGB.)
Let's say your client's brand colors are defined in sRGB color space, then I guess you could create a sRGB document in Photoshop (when creating a new document you get to choose under Advanced), create color patches of the colors you need, and then "Convert to profile..." under the Edit-menue. Choose "HD-TV (Rec. 709)" as target color space (if that's your target).
Now the patches have different RGB-values but will look exactly the same (or as close as possible within the limitations of what colors can be defined in that color space).
Then use the magnifier tool* to pick up the colors, which now has other RGB-values but when showed "through" the Rec 709 color space should look on the screen just like they did in sRGB & Photoshop.
* Haven't tested this, if it doesn't work I would use the pipett (or whatever it's called, I'm using a swedish Photoshop :) ) to pick up the colors within Photoshop and write down the new values. Or save as an image file, import into FCPX and then use the magnifier.