Complex sentence: Even Stormy is confused, but assured that she isn't the cause, Rainbow and Starlite return to Colorland to find its vividness has dimmed, as well as finding their friends, the Colorkids and Sprites, are weak and seemingly dying.
Split into simpler sentences: Even Stormy is confused, but Rainbow is assured that she isn't the cause. Their they find their home's vividness has dimmed, as well as finding their friends, the Colorkids and Sprites, are weak and seemingly dying.