Making these little swatches is a great exercise. You can do something similar playing with coloured pencils and graph paper, but it's not the same as seeing the stitches.
As you keep going, you get ideas about developing the pattern, as shown here. Adding a checkerboard background to the multi coloured hearts makes 'em stand out. Doing that led to more hearts, but these ones squashed up together. You're made aware of the space between the motifs - in this case, small squares. Should they be cream to make them merge into the background? Or a bright colour to draw attention to their shape?
As I type this, it's pouring with rain outside. I'm venturing out for my painting class this afternoon, so fingers crossed it clears up. Oh well, it's filling the reservoirs and gives me a great excuse for not tending my allotment!