There are two aspects to it.
If you're talking about the B&N OS UI then it's B&N who have done the decisions. That isn't changeable - as far as I know. There might be a high contrast option in settings. Actually there is. Check it out.
If you're talking about Apps then Apps use the Android guidelines. And sometimes it isn't very readable, unfortunately.
I wondered if the UI was simply set by B&N, but I thought I'd ask, in case I was missing something. It's a minor thing, hardly a deal breaker. Overall, I can strongly recommend the HD! I'll play around with the contrast option and see if that improves things. Thanks for your reply.
Can can you tell me where the option to increase contrast is located? I'ver been unable to find it on my HD+.
OK, sorry - It's only for the browser.
If you go to Settings > Applications > Browser
Then click on Accessibility, there are some options like Text Size and Inverted Screen rendering. Also Contrast. You can increase contrast from 100% to 300%.