Spotting

thanks Chester!! Since I had seen yellow aphids recently I was not sure whether it was Aphids you had. Cool spotting. Shows interaction between two species and how they benefit each other.
Yellow Aphids on milkweed in this spotting,
http://www.projectnoah.org/spottings/130...

I believe you meant "protect the aphids". Yes Emma they come in many different colors, think the only color I have not seen is blue.

So aphids come in different colors?
The ant does not harm or eat the Aphid?

The picture shows ants tending aphids. Aphids exude a sweet liquid called honeydew. They provide it to the ants, which in turn protect the ants.