Looks like COLORTERM has gone out of fashion.

src/jit/dump.lua

@@ -644,7 +644,8 @@ end
 local function dumpon(opt, outfile)
   if active then dumpoff() end
 
-  local colormode = os.getenv("COLORTERM") and "A" or "T"
+  local term = os.getenv("TERM")
+  local colormode = (term and term:match("color") or os.getenv("COLORTERM")) and "A" or "T"
   if opt then
     opt = gsub(opt, "[TAH]", function(mode) colormode = mode; return ""; end)
   end