difference between Metal and OpenGL texture sampler?

Hello,

I'm trying to port an old project to Metal from OpenGL. It is working pretty much, except that the values I am reading from my Metal texture sampler seem to be different from the ones I get in OpenGL. For example, where the OpenGL version is giving me green values of .5, Metal is giving me about half that. The values aren't exactly half though, they are a little higher than that.

Anyone know what would cause that? Some adjustment by the MTKTextureLoader maybe? I've tried fiddling with my min/max and mipmap settings but that doesn't seem to be doing much.

Here is the OpenGL version (ignore the green, I'm just dealing with the fonts right now):

https://imgur.com/CBwC18g

Here is the Metal version:

https://imgur.com/h7jBMrF

Thanks

Bob

ps why did Apple remove the ability to upload images? It's such a pain to upload them to a third party site and then get a link.