When you look at development times between B&W films the development times vary when the speed of the film varies. For example:
- Ilford FP4 Plus with HC-110 dilution B at 20 degrees takes about 9 minutes for development.
- Ilford HP5 Plus with HC-110 dilution B at 20 degrees takes about 5 minutes.
But the development times of Kodak Ektar 100, and Kodak Portra 400, using Arista C-41, at 39 degrees, are the same, 3:30 Mins. Or when you choose Tetenal C-41 it is 3:15 Mins.
Why is it that the color development times remain the same?
Edit: This applies to ECN-2 an E-6 as well. As mentioned by @timvrhn