The available resources are fonts (text, menu), foreground, background (text, menu, bottom dialog), displaywarning and geometry. Here is a simple .Xdefaults portion for Xcoral:
xcoral*geometry: =600x500+200+100 xcoral*background: midnightblue /*text window background*/ xcoral*foreground: darkseagreen1 /*text window foreground*/ xcoral*font: 9x15bold /* text window font */ xcoral*mbg: lightslategray /*menu background*/ xcoral*cbg: lightslategray /*control panel background*/ xcoral*displaywarning: True