Is "Dragons" an appropriately narrow category for the background skill Lore?
Lore (dragons) is too broad
The description of the skill Lore in Background Skills on New Skills says
Lore skills normally can’t be used to identify monsters the way Knowledge skills can, unless they refer to a specific type of monster (such as owlbears or vampires). If Lore involves a common, broad category of race or monster, it needs to be more specific. Lore (elves) would be too broad, as would Lore (dragons).
(Emphasis mine.) Thus Lore (dragons) would be inappropriate for most campaigns. Since later the Lore skill description says that Lore (frost giants) is acceptable but Lore (giants) isn't, Lore (gold dragons) will likely be met with less resistance than a broader category like Lore (chromatic dragons).