Consider this very basic title slide. It has a rather simplistic design with a plain warm yellow background and a simple title with caption. The left side certain stands out and is attention grabbing, but does the text really attract you to continue viewing? The right side feels less jarring, but seems more comfortable to look at?
The choice of font color depending on the background is a difficult but very crucial component to making compelling designs. This applies to making thumbnails for YouTube videos, designing slideshows, posters, and more. The designs become increasingly more difficult as the background becomes more complex, and the number of contrasting background colors increase.
However, just starting from the basics, a key component to choosing a single font color on a solid background is the contrast between colors. The color wheel is a good starting point, where adjacent colors tend to lack sufficient contrast for the text to stand out, and complementary colors create strongest contrast. However, too strong of a constrast may be jarring, so finding the balance bewteen the two involves experimenting, some careful calculations, and perhaps a useful guide.
I came across this article which provides a relatively straightforward but detailed guide on the contrast for this purpose. It tackles the problem from a few different directions and provides some helpful examples. If you are stuck about how to choose font colors, perhaps this is a good starting place.
