I'll give it a shot...

How about Ranitomeya amazonica "Arena Blanca". No orange, but bright red like you see in several of the images in a Google image search.

I do believe though that the frogs that meet your criteria are extremely small and also very drab compared to the more common frogs. I can't recall the genus or species of any of them off the top of my head but I'll try and find a page I came across last year that discussed hard to find PDF's.