"much more colder" is incorrect, because you can't use "more" and -er together. "much more" is not stronger than much, it's just the comparative used for 2+ syllable adjectives that don't end in -y In other words, "X is much prettier than Y" = "X is much more beautiful than Y" (same meaning). To make your comparative stronger, try these: "X is far colder than Y" "X is way colder than Y" (informal) "X is much, much colder than Y" (informal) "X is so much colder than Y" (informal)

Monday was cold. Tuesday was colder, but today is definitely the coldest days.

X is colder than Y X is much colder than Y X is so much coler than Y

Thanks

the latter one