I'm trying to make an image in Blender using the cycles engine. When I choose rendered in the view port shading menu, there's color. But when I actually render it, it's in black and white. What do I do?
What are you trying to do with the dilate/erode node?
That is what is turning your image into B&W.
Remove that node and your image is fine:
The Dilate/Erode node expects an input of a single channel (not RGB), and will output a single channel as well: a single channel will be a Black and White image.
The Dilate/Erode's node is mostly used is to expand or contract the edge of masks.
To work with a color image (RGB), you would need to split the channels of the image, and use dilate/erode nodes on each of the channels of the image. Then the channels can be recombined, as in thid example from the blender manual
But I suspect that you are looking for a way to create some glow... Use the Glare node instead.