Ian, nice work, and a couple of questions on your calcs if you're still listening.
As you indicated, you're taking the quoted Coopers IBU spec and adjusting by 1.25/23 (that is, for a 23L brew). But when it comes to colour, you're using 5/80. For Black Rock, on the other hand, it's 5/80 for both colour and IBUs. Why the difference?
Then, having adjusted the kit colour for volume in the "kits" tab, it looks to me like you're doing it differently in the "main" tab in rows 100+, using a constant adjustment of about 87% of the first figure. For IBUs, however, the "kits" and main" figures are identical. One again, why the different treatments?
More generally, I am having difficulty following your colour formula. This is something I have been looking for a for a while for my own spreadsheet, for all-grain. As far as I can tell, you are saying colour = 1.4922 [lbs * SRM/US galls] ^ 0.6859. Where do those parameters come from? It is interesting that this is a non-linear formula, ie, three times the grain, or the same amount of a three times darker grain, does not mean three times the colour. Can you point us to a source for more information or more discussion of this point?