That can happen!
Unfortunately the ink that is inside the LT Cyan cart will never be light enough to function as a Lt Cyan. You could remove the fill hole plug and draw out the ink and put it in the drain (non-toxic and you do not want to reuse it) - or give it to an artist as an excellent and strong drawing ink.
Take a syringe and suck the ink out of the cart.
Now - some Cyan in a Lt Cyan cart will darken the Lt Cyan when you put it in. So - maybe the best thing to do after it is empty(ish) is to put some distilled water (NOT TAP) inside the cart and shake it and then drain that out. A few drops of distilled water in Lt Cyan ink would not be as bad as a few drops of Cyan ink in Lt Cyan.
Hope this helps you!