I'm trying to make the com_sfx_contrail effect not be transparent at all, and I want the colors to be the same as my texture. how can I do this? I'm confused as to which settings do what, as there are multiple color hue and alpha llines.

For all color fields (spawner and all transformer stages), set all RGB values to 128. That will make it so it doesn't discolor your texture. In the spawner and the transformer stage 0, set alpha to 255. Then set the other transformer stage(s) to whatever you want. That should get the result you want, if I'm understanding you correctly. I looked at the effect in particle editor and when it's set as a streak (which is what it should be), it doesn't show up at all, so I can't say for sure.

is there a way I can make streak repeat my texture instead of stretching out a few pixels?

I don't think you can do that in particle editor. Instead, you could increase the size of the texture and tile it.