Assertion:
Netscape versions 2.0 and above have a small idiosyncrasy relating to background images with this element. The background image of the document (if one is specified) is not used inside a square region surrounding the radio button. If the document has a background color, it is used in the "non-radio" portion of this square instead. This does not happen before Netscape 2.0 - it appears that form field rendering was changed for version 2.0.

BODY uses BGCOLOR=red to create extreme contrast to exhibit the behavior

TABLE with cellpadding=20 and background="tilepattern.gif" (extreme contrast to help see the behavior):
filler text
TD Cell 1
Radio button:     
Checkbox:     
File:     
TD Cell 1 		TH Cell 2
Radio button:     
Checkbox:     
File:     
TH Cell 2
filler text