Color management - How to identify saved color in TIFF

[IcePlanet]

Somehow I still do not understand how colors are processed inside GIMP. Let me explain my question on one example.

I run into 'easy' task to identify color in TIFF file. Each application I used shows different values. To identify what is going on I made simple test scenario. In Corel Draw created simple image with 2 colors (CMYK: 85/30/0/100, Pantone 186C). Exported this image to TIFF and opened it in:

GIMP - 0/0/0/100 and 0/100/88/11 respectively.
CorelPhotoPaint - 85/30/0/100 and 2/100/88/9 respectively.

I have read (here) about checking color profile, and there is set relative colorimetry, CMYK profile: None.

My question is: What colors are inside the TIFF? How should I understand the different values in different programs? For now please ignore different 'render' on the same screen, which initially triggered my curiosity, but I understand this is related to CMYK - RGB conversion where much more elements are included and more or less no standard exists, but was thinking that value inside TIFF is the same regardless of used program. Or not?

GIMP is version 2.10.24

I added pictures to google drive, there are 3 pictures showing eyepicker tool and corresponding colors (visual representation of the above text).

Thank you for explanation

[rich2005]

Do not be surprised at differences between applications. If you search you can find reports of differences between PS and inDesign and they come from the same company.

I do not have CorelDraw so this is using Krita in CMYK mode: https://i.imgur.com/b79XRA7.jpg Pantone are spot colours I make 186C this https://mypantone.info/186C.html

Exporting as a tif and opening in Gimp I get this: https://i.imgur.com/yzuZJ21.jpg and it is not that far away from values used in Krita. Values showed using sample points.

Using a plugin (Cyan) I can import the tif file and assign a RGB profile. https://i.imgur.com/Sii4sDh.jpg Not surprisingly the values are different. Colour profile does have an effect. https://i.imgur.com/imbTpD5.jpg

Even worse, If I soft proof that, your colours are out-of-gamut https://i.imgur.com/PShm7yV.jpg
but then that all depends on the profile used for soft proofing and Gimp is not very accurate, it is after all a RGB editor.

It is a good question, truthfully I do not know how the internal RGB - CMYK conversion is made, you could ask the question over on https://discuss.pixls.us/ where there are people more into printing.