Verified answer

Sewing would be easiest.

Go to a thrift store and buy a lightweight black shirt and a white shirt that are nearly identical.

Cut both shirts down the middle and then sew a black half to a white half (pretty much straight seams).

Do the same with two pairs of lightweight pants or drawstring pajamas - the pants would really have to be almost exactly the same so that the seam would be easy to match up.

The EASIEST way would be to get a white shirt and white pants...and some black RIT dye.

Mix up the dye, then just dip the half you want black into it. Be VERY careful when dipping...but this method only takes about 3 minutes total...from mixing to dipping.

Hang the items up to dry overnight, then run it through the dryer on the hottest heat possible to set the color. If you wash it before setting the color, it will fade and you'll be left with a white and dark gray costume.

The best way would be to sew together two identical shirts in different colors, cut them in half, and sew them together. You could also do this with one shirt by buying it in white and dying one half black after you cut it.

If you really don't want to sew, the cleanest way would be to use fabric paint to paint one side black. This would be time consuming though, and would make the fabric really stiff.

You really should just sew it! Borrow a friend's or relative's machine. It's only two straight lines :)

If you don't want to sew just use fashion tape, fashion glue or hot glue to secure the shirt and pants back together after cutting one of each color in half. (Folding over cut edge slightly before securing will hide the raw edge and prevent fraying)

Idk