Lab Values changing RGB values

[Mr Curieux]

Hello community,

I am facing this struggle too often and Iwould like to understand. I have created a series of color palette for my designs (CMYK - Pantone - RGB), but whenever I load my Pantone palette into any new file, they get converted into Lab (sometimes some colors remains in RGB other change to Lab). I am making sure that all of my files are in Adobe RGB 1998 color profile.

Lab values change my color quite a lot and it is rather annoying to have to correct those each time.

Left side is my Pantone swatch in RGB as spot color and on the right is the same color copy pasted into a blank new RGB document.

Below is the result of the RGB conversion... 

If anyone can explain this mystery...

Thanks!

[Ton Frederiks]

The Pantone colors are defined by Pantone as Lab colors.

CMYK or RGB are just simulations of a Pantone color ink mix and will vary with the ICC profile for the active CMYK or RGB profile. 

If you select a Pantone color in Illustrator it uses the Book color (Catalogue de couleurs) as defined by Pantone.

The Lab values are the only correct values for a Pantone color, al others are simulations.

[Mr Curieux]

Hello Ton,

Thanks for your quick reply!
Now I understand better the differences between the Lab and RGB.

But I just made a quick test on 2 files.

Left are the copy pasted colors into a blank new document (both using Adobe RGB 1998).

Righ is my color palette file.

On the right side, all colors are set to have RGB values, and my own Pantone values are the one from my Pantone book which I bought last year.

Once copy pasting them into the new document on the left, I notice that the Illustrator Pantone keeps their RGB values, while mines switches to Lab, and as you can see for the magenta is does change the color nuance.

Do you know why is there more "stability" between the Illustrator default swatches as opposed to the one I created?

Thanks a lot!

[Test Screen Name]

Lab colours should be more accurate. You need to look at how you view and measure your RGB colours, which look diffferent for everyone. 

Is your screen calibrated? What RGB profile do you use?

[Mr Curieux]

Hello Test Screen,

My RGB color profile is Adobe RGB 1998, both on Illustrator and as ICC profile for my external screen. At home my external screen is calibrated using a software (Lenovo Thinkcolor).

But to be honest, this whole thing is really difficult to grasp... At my work I have another screen, and there the colors looks duller. I try many color combinations, and it always looks like my laptop screen is at the end brighter than the external screen.

[Ton Frederiks]

Lab colors (and Pantone ink colors) are better displayed when Overprint Preview is active.

With the normal preview they display as their document color mode equivalent.