Get a new evening dress?

Browsing through sis's old post in her blog, saw her wearing a blue-ish and green-ish (don't remember the specific name for that colour) dress she wore for her college night ball. Reminds me the brown dress I saw in Asian Avenue. Liked it at very first glance. Thought of buying it but......probably won't be wearing it anytime soon since no formal night function at my college. Never heard any of it YET. Hard to find one when you needed it most but easy to find when you dont need it at this point of time.............. Buy or not buy? =/