They're both correct.
If you're thinking of candy as 'stuff' ( a product/substance), you can use the singular form. If you say "A lot of candy is pink", the word 'candy' is an uncountable noun.
If you're thinking of candies as 'things' ( individual objects or types of objects) ,you can use the plural form. If you say "A lot of candies are pink", the word 'candies' is a countable noun.