Signatures: restrict color to backtrace printing (#41929)

Fixes #41928

Author: timholy

base/show.jl

@@ -2378,7 +2378,9 @@ end
 function print_type_stacktrace(io, type; color=:normal)
     str = sprint(show, type, context=io)
     i = findfirst('{', str)
-    if i === nothing || !get(io, :backtrace, false)::Bool
+    if !get(io, :backtrace, false)::Bool
+        print(io, str)
+    elseif i === nothing
         printstyled(io, str; color=color)
     else
         printstyled(io, str[1:prevind(str,i)]; color=color)

test/show.jl

@@ -1377,6 +1377,11 @@ let m = which(T20332{Int}(), (Int,)),
     mi = Core.Compiler.specialize_method(m, Tuple{T20332{T}, Int} where T, Core.svec())
     # test that this doesn't throw an error
     @test occursin("MethodInstance for", repr(mi))
+    # issue #41928
+    str = sprint(mi; context=:color=>true) do io, mi
+        printstyled(io, mi; color=:light_cyan)
+    end
+    @test !occursin("\U1b[0m", str)
 end
 
 @test sprint(show, Main) == "Main"