a common way to tell other than size and the difference in blues is the yellow around their beak! lear’s have a wider yellow patch on their lower beak (hyacinth is second pic)
lear’s macaw, closely related to hyacinth macaw and people mix them up a lot! hyacinth is the largest flying parrot about 40 inches long while lear’s is roughly around 20-30s. their color is different aswell with lear’s being more green grays undertones and hyacinth a rich blue