Opal is a great beginner colorwork sweater. Only two colors at a time are utilized throughout and only a few rounds have floats that are long enough to need catching.

Choose two colors that have good contrast between each other for the yoke and pick a third complementary color for the rest of the sweater.

Try out different combinations when swatching to experiment with the two contrast colors - starting with a dark color rather than a light one can create a very different effect for the yoke.