I read this fill-in-blank question on the CD ROM attached to one of newly- published English grammar books by an English linguist:
It's very chilly today, but I think it was ____ yesterday.
And the given answers are: colder/ more cold.
I searched the reference.com web for "it was colder''/"it was more cold", and the results are 3880/79. Then can we say "it was more cold yesterday"?
You can, but it is not as fluent as "it was colder".