Why would a tiny frog be a bright, bold colour instead of hiding?

Deep in the rainforest sits a frog no bigger than your thumbnail, glowing electric blue, or blazing red, or golden yellow. Every other small creature around it is trying hard to blend in and not be spotted. This frog does the opposite: it practically shouts 'here I am' to every hungry bird and snake. So why would a tiny frog wear a bright, bold colour instead of hiding?