As known dragons are not necessarily enemies of each other despite different alignments.
What I am wondering is are there any known instances of friendliness or friendship between chromatic and metallic dragons?
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While not from 5e, the 2000-2002 Dragonlance novel trilogy The War of Souls contains an instance of 'friendliness' between Mirror (Solomirathnius), a silver dragon and Razor, a blue dragon. They work together for a while since they have common goals and do not attempt to outright kill each other.
The answer by Karan Shishoo is probably more in line with what you have asked for, but since you asked for generic lore, let me add the following:
There is an entire 2e campaign setting called the Council of Wryms, initially published as a boxed set and later as a hardcover book. The setting is located in its own crystal sphere, and the main location is a chain of islands called Io's Blood Isles. The Isles are ruled by a council, with dragon clans of 15 different dragon types (5 chromatic, 5 gem, 5 metallic) represented democratically. Dragons do not war against dragons, and disputes are resolved at the council.