Good morning,
A very interesting question.  From your question, I understand you received new complete dentures and were charged for a lighter shade of tooth.
If you received a partial denture and an existing natural tooth needed to be filled or crowned, then the cost of that particular tooth would be different and possibly higher, but if you were charged simply for a lighter shade of teeth in new complete denture, that’s a different matter.
In the dental industry, there are many manufactured brands of false denture teeth, and within those manufactures, there are many, many sub brands of teeth.  In those sub brands, there are several,  usually all of different names, of denture teeth.  Also, aside from different shades or color values of teeth there are several different density selections and shapes or molds.
All this means to you is that,  after properly diagnosing exactly what type of denture you needed, the practitioner has a large range of choices as to which teeth to use, what shape they should/could be and what color they should/could be.  All of this should be discussed with you either in some part before you start the procedure, but definitely during  the procedure, well before the dentures are finished.
Having said all that, when you were quoted the cost before you began, the practitioner should stick to it, unless something unexpected came up or he or she has a very good reason to alter the initial cost quoted to you, but,
no matter what manufacture , brand and sub brand was chosen for you, the color or shade selection within that selection would be the same for what ever color was chosen.   For example,  If manufacture A was chosen, then brand B was chosen, and sub brand C,  all the colors available to the practitioner in sub brand C, which could be anywhere from about 10 to 40, would be the same cost to for the practitioner to purchase to make your denture and the same cost to you.
So, If you are certain that you were charged for simply a lighter color/shade, I would definitely ask your practitioner why this was done, and exactly for what were you charger extra for.  There could have been simply an account mistake made,, but regardless you need to know what you were charged for, and if a mistake was make, allow the practitioner to remedy the mistake.
You as a patient must be treated with respect and fairness, and not be taken advantage of.
I hope this helps answer your question, please write in again with any other concerns.
Thank you,