Sorry Annie
I really don’t know what to tell you. The hardest thing is to troubleshoot a problem that you can’t re-create on the test bed. I am not having any problems here with either the black and white or the color captcha.
Something has changed on your side. If I knew what it was I could recreate it on my test bed and develop a workaround.
Testimonial basics generates the captcha in a php file in the includes directory. The image is created using the GD Library and what I am seeing on this end is it can’t access the url (php file) it needs. If you are preventing access to the testimonial basics plugin files that may be the problem.
Kevin