Color Management: How to specify Colour

[Dewcal]

I was recently asked to supply a figure on a specific background colour to allow a seamless insertion into a web site. The colour I was asked for was "#C0DFFD" so I duly filled a layer in PS using the Paint Bucket and typed in the above code into the colour picker and sent off the image.

I was then told that my colour was incorrect and the web designer had to select the background and "re paint" with the correct colour.

On comparing his colour picker with mine, numerical differences can be seen and I would appreciate it if someone could explain why these occur when the # number is the same?

He is using CS2 and an uncalibrated monitor compared to my CS3 & calibrated. I also use the ProPhoto workspace (but had saved to sRGB).
The figures are -

Both had #C0DFFD

His - Hue 210, S 24, B99 - R 192, G 223, B 253, L 87, a -6, b -18, C 27, M5, Y 0, K 0

Mine - H 209, S 24, B 99, R 192, G 223, B 253, L 89, a -20, b-19, C 33, M0, Y 3, K 0

As I had naively assumed that the "#number" specified all aspects of the colour, can anyone advise how I can avoid these kinds of problems in the future?

Any help would be appreciated.

Dave

[igot2pman]

#C0DFFD
CS4 - H 209, S 24, B 99, R 192, G 223, B 253, L 87, a -6, b-18, C 22, M 5, Y 0, K 0
My old CS3 had the same numbers, but I may have copied them over when I installed CS4. I wanted to keep my settings and stuff so I copied alot of things over.


His number was (CS4):
#bed8f1

Things should be the same, odd. It would have nothing to do with the monitors as it is PS's number values. Maybe things changed. It makes you wonder if you type the numbers exactly, if you would get the same color...now here the monitor calibration would come into effect.

anyway, good thing to look out for.

[Dewcal]

Thanks for reply - good to see CS4 = CS3!! Agree that it "should" have nothing to do with monitors etc as that should just affect appearance equally to the "same" colour. I can understand a slight difference in CMYK values as dependant on the board stock selected in colour preferences.
Still puzzled.

[Michel B]

Dave, I am not a color expert, but the same numbers in different color modes refer to different colors. So, if you created your background in prophoto, the color had to be different. Just try to convert to sRGB before adding the background and setting the numbers.
Do this: create the background in a separate file in sRBG. Convert to prophoto and look at the new numbers. Now use those numbers if you want to create the background in prophoto. Chances are you'll get very close. This color should not be out of gamut since you first defined it in sRGB.
Anyway, if you are working for the web, I don't see any advantage with using a larger color space.

[Dewcal]

Michael,

Thanks for the enlightenment! Have tried what you suggested and can see the difference. Obviously need to know what colour space recipient is working in as well as colour required.

As for working in ProPhoto - most of my work goes to print and this web request was a one off.

Thanks again.
Dave

[Dave.Cox]

The hex color number #CODFFD is a hexidecimal represtation of the RGB values, where #C0 = Red 192, #DF = Green 223, and #FD = Blue 253. Even when these values are set the same, changing color profiles in photo shop can change the conversion values between the RGB mode, and the other modes, and the conversion formula changes. That is why you can see a difference if you have a different color space (or color profile) selected. So it's true, changing monitors will not affect the numbers. But if you have a calibrated monitor using a stored color profile, the the color space may be different. As a result, if you are not both using the same color space, you may get some differences. The best way to avoid this, is to make sure you are both using the sRGB color space, as Michael B pointed out.

[Dewcal]

Dave, Many thanks for the detailed explanation - like many things, obvious when you understand! I was guilty of assuming that the #number crossed colour spaces and smaller colour spaces had "fewer" discreet #numbers.

All help has been much appreciated.
Dave