diff --git a/matlab/matlab-quiz.md b/matlab/matlab-quiz.md
index 5f5976421b..686e4005cb 100755
--- a/matlab/matlab-quiz.md
+++ b/matlab/matlab-quiz.md
@@ -895,3 +895,10 @@ a =
 - [ ]
 
 [Reference](https://mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html)
+
+#### Q56. You've just plotted some data and want to change the color behind the lines you've plotted to black. Which code block will accomplish this?
+
+- [ ] `h_f = figure;  set(h_f,'Color', [0 0 0]);`
+- [x] `h_a = gca;     set(h_a,'Color', [0 0 0]);`
+- [ ] `h_a = axes;    set(h_a,'Color', [0 0 0]);`
+- [ ] `h_f = gcf;     set(h_a,'Color', [0 0 0]);`