I've tried using a outline shader I found online but it didn't work with the line2D it just made the line be white. It seemed to coralate with taking the texture using the Uv, but I'm unsure how to go about making a outline shader.

Help on how I would go about doing so (or any in general) will be appriciated!

How often are you planning on using an outline effect? Is it for all your sprites? It would take a bit of work but what I would consider doing since it's 2D sprites you're dealing with would be to draw an outline myself as a separate sprite and have it white rather than any complicated shader trickery. This way you could change the colour however you want in the engine, is there a specific reason you're trying to go for a shader?