alt text for image showing

[letsgofishing]

Some help if possible please.
I've got a portfolio page with images that have image captions (alt text) so that search engines "see" them.
They are pop up images. However, I don't want the caption to show after you've clicked on the image.
In the pop up photo options panel, i have NOT checked the "show image title" box, but they still show on all the images when they pop up.
I've attached a screen shot.

Secondly, still with pop up photos, I check "dim page while op up is open".
Is there any code that can be inserted to make the screen (background) black - or white?

Many thanks,
Mike