That's the way it is. The image has been superimposed on an actual button. At least, that's what I think is happening.
There's an attribute that is implemented for the <tdbutton> token, that I inadvertently omitted from the descriptor file, so if you use the "Insert Token" dialog from the Cell Dialog, you won't see an option for using a "link" instead of a button. Sound confusing? Does to me, too.
OK, your <tdbutton> token probably looks similar to this:
<tdbutton type="nextround" image="C:\Program Files\The Tournament Director 2\images\right-arrow.jpg">
Insert the "link" attribute like this:
<tdbutton type="nextround" image="C:\Program Files\The Tournament Director 2\images\right-arrow.jpg" link="true">
This will make it behave like a link instead of a button, and should remove the "gray" around the image. Of course, this also removes the "push" effect of a button, but that may not matter to you.
Alternatively, if you want to keep the "push" effect, you can change the styles of the button to remove the gray:
<tdbutton type="nextround" image="C:\Program Files\The Tournament Director 2\images\right-arrow.jpg" style="border: none; background: transparent">