I believe your profile is inaccurate. But that's fine, there's ways around it. (lets hope your profile gamut isn't limited before the colour you're trying to create as sometimes when creating a profile, you can do some things wrong and the colour gamut will be smaller than what the printer can really do)
You'll need to do your colour management though illustrator, not onyx (the way you're trying to do it, even though that's the right way)
If you know onyx is printing the colour lighter (or darker). Go into illustrator, create a patch with the current yellow you're using. Then create patches darker (or lighter) than the yellow. This will be all guess work. And hope it comes close to what your need it to be.
I missed this earlier. Are colors are as close as you can possibly get to true accurate colors lol. We have invested in a lot of equipment along with thousands in training and have been color certified along with our colors certified by the 14 college collegiate licenses we have to be dead on for its a nightmare in the end.
I am not having an issue with the color persay. I cannot hit the color out of illustrator as it consists of a specific mixture of orange that illustrator will not allow me to achieve.
In this situation i am able to get close enough out of illustrator for it to be ok but the problem i was having was simply trying to find a solution to the color change in onyx when using a shadow or a transparency not about printing a specific color.
Hope this made more since. The orange i need to use is a color that i created a while back when using printed swatches out of onyx. I have the mixture set aside to do a color change in onyx and i have done it a few times but on this particular print i would like to use that orange but it has a shadow in the image.
I was able to get a close orange that the customer is ok with im just simply trying to figure out how to do a color change in onyx with a shadow.
I think i repeated myself sorry.
