2-dimensional ray tracing
Python, 602 559 614 chars

import sys
S=sys.stdin.readlines()
X=max(len(s)for s in S)
I='#'*X+''.join(t[:-1]+' '*(X-len(t))+'\n'for t in S)+'#'*X
L=len(I)
R=range(L)
B=[0]*L
C=[0]*L
for p in R:
 if'@'!=I[p]:continue
 for d in(1,-1,X,-X):
  q=p;c=7;b=100.
  while 1:
   q+=d;a=I[q];B[q]+=b;C[q]|=c
   if a in'\/':d=(ord(a)/30-2)*X/d;b*=.8
   elif a in'RGB':c&amp;=ord(a)/5-12
   elif a in'&gt;&lt;^V':d={'&gt;':1,'&lt;':-1,'^':-X,'V':X}[a];b/=2
   elif' '!=a:break
print''.join(I[p]if' '!=I[p]else' bgcrmyw'[C[p]]for p in R[X:-X])
i=0
for p in R:
 if'?'==I[p]:i+=1;print'#%d:'%i,'%.0f%%'%B[p],[0,'Blue','Green','Cyan','Red','Magenta','Yellow','White'][C[p]]


Edit: fixed so it doesn't need trailing spaces.