Most of what you have plant are at very early stage. But I have a few questions an comments:

How big a growing bag(or whatever) , in gallons you have for squash and tomato?

Planting a single corn , in a bag probably is not going yield anything.

Most winter squashes need big room for their vines to run. Unless you have planted bush type.

What kind of tomato have you? is it determinant, indet, bush/dwarf , ??? I have not done container planting but for example for small det. type tomato plant you need a container w/ min. five gallon soil capacity and min 12 inches depth. Some other might need over 10 gallon soil. Squashes will need just about the same or even more.

Yet another issue is the medium. For container planting you will need SOILESS medium.

Is your tomato plant still in the nursery pot? It looks like it . And the reason for purple color is that it is root bound and just suffering from mal nutrition.

Apparently there are now bag pots for gardening. Us in-ground gardeners can't keep up!

Your mixture has its possibilities, but I don't know if it is well-suited for vegetables.

Some of the colorings could be due to the variety of the vegetable; purplish tomato and reddish corn plants may not be unusual. If growth appears stunted, try some liquid fertilizer.

The butternut (a winter squash) is too young to be worried about.

Try posting on the Vegetable Gardening forum also.

also look at the container gardening forum...SO much info that would help you :)

The tomato looks to me likes its had too much water. The corn stalk looks normal, mine are all red at the base too, probably the variety. But again the corn leaves look like the plant is too wet. I thnk you need to check the drainage of your container.

I'm not a big fan of potting or garden soils that are sold at the big box stores. Many of them can contain ingredients other than soil, they may have unknown chemicals, etc.
Best way going forward is to start composting and mixing the finished compost with either peat moss or coir, with a bit of sand or perlite for drainage. Here in the northwest we have access to a lot of seaweed as well, which makes a great soil builder. Make a seaweed tea then compost the seaweed afterward.
Above all, you need to get lots of minerals and active microbes into your soil.
BTW-if the tomato problem is not too much water, it may be too little mineral. Try a tablespoon of Epsom Salts when you water and see if the color starts to improve.