Sampling a specific color

I’m looking for a more efficient method of using a line trace to sample the color of the pixel/texture that was hit. The texture is a RenderTarget, and right now, the only method I know of is to use ReadPixels() to store and iterate through all of the pixel data. The RenderTexture is always changing, so this approach is massively inefficient because I have to fetch all of the texture data off the renderthread every time, causing a large hitch/freeze in the process. Surely, there must be a more to-the-point method of getting the color of the one pixel that is traced. Any pointers are appreciated.