Renders in greyscale

I’m not sure why this node setup is causing the render to be black and white. The materials look as intend in view-port shading. I’m pretty sure it has something to do with the colormix node but I’m not sure what or why this is the case nor how to fix it.

Always mind the color coding of the nodes’ inputs and outputs: They are there for a reason.
The green output of a BSDF node must ALWAYS and only be connected to a green input. In your case you’re connecting green to yellow, which does not work.

Either mix shaders (green connectors) with the Mix shader node or mix colors (yellow connectors) with the MixRGB node. In your example you could just delete the Diffuse BSDF node and connect the color texture directly to the Multiply node.

You cannot mix a shader with a texture. Unless you have transparency in a color ramp(that you do not in this case), Alpha output will be completely white, so that connection makes no sense as well.

Thanks, I replaced the shader node with a RGB node.

edit: and then I quickly noticed the mix node can output color without input

It seems to me you are doing random stuff. That is a great way to learn some things, however I do not believe Cycles nodes and materials is one of them. I would recommend reading about what nodes do what and watching some tutorials about making materials. If you have AO texture and color texture you likely want to just multiply them together with color mix node and maybe adjust the tones of the AO texture if that’s needed. It’s possible to do that with color ramp node.