Printers don't print white ink, so when using transfer paper for lights, anything in your design that is white will be the color of the t-shirt when pressed.
For the colors you're using, dark transfer paper is the way to go. But because of the entire sheet gets applied to the shirt, you need to trim around the design to eliminate any area that is not design.
If what you're doing is just lettering, I suggest you use either cut vinyl or plastisol transfers.
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