If you don't know what the final color is supposed to be, then go by feel.

Stripes can show up long before the fruit is ripe.

You will not get a mix of fruit colors on the plant. All the fruit on one plant will be the same, with exceptions for things that are influenced by environmental conditions. But all the fruit that matures at a given time will resemble one another. Some varieties can look pretty different at different stages of ripeness, leading to the impression that there are different color fruits on the plant, but that's just fruit at different stages of ripeness.

Pictures would help.

How are they supposed to feel?

There will be a period of trial and error at first to determine when the ideal point of ripeness happens. But that happens with all tomatoes, as varieties are all different when it comes to how ripe is perfect vs. underripe or overripe. But if you don't know what a tomato that is generally ripe is supposed to feel like, you can compare it to the feel of ripe red tomatoes at first.

Did you make the cross yourself? Is that F1 BKxBTD? If so it should probably be a red with stripes (not really sure what color the stripes should be though, probably orange). It will definitely look different when ripe. Never had a tomato that wasn't clear when it's approaching ripeness, including GWRs.

These are bought seeds from Marianna's, Brad Gates.

How long does it take a mostly grown tomato to grow ripe? I have about 20 tomatoes on 4 plants, but the colors don't seem to be changing much. Some have been there almost 4 weeks.

The ones on the two BK x BTD are decently big and dark green with stripes, but still feel quite hard.

http://feldoncentral.com/garden/tomato_timeline.html

BK x BTD will most likely be a black (which in tomato parlance means something like dusky dark pink/purple, maroon, and/or brownish red) with stripes. But why don't you ask your seed source what the final tomatoes should look like? When crossing 2 stable varieties in a controlled fashion, the F1 traits are generally pretty well known. It's not until F2 that things get wildly unpredictable.