Few things you can try.
First- if you're talking about the Workout app, you can use the Digital Crown to select a metric and hilight it. This makes it a bit bolder and colors it to make it more visible.
Second- if you find a lot of text on Apple Watch hard to read/see, you can turn on Bold Text. On your iPhone, open the Watch app and go to Accessibility and turn on Bold Text.
Thirdly- you can try using Zoom. It's located in the same area as Bold Text.
Hopefully one of these three options help you out! You can find more information about the later two options here: https://www.apple.com/accessibility/watch/vision/