Check to see if you accidently altered the opacity. Right click on the item in the timeline and select properties, then find opacity in the properties box. You probably want it to be 100%.
Welcome to the forum.
Along the lines of the above response, look at the orange-yellow line (rubberband), that runs through the Clips. Compare its position in the "good" Clips, to the position in the "bad" Clips. They will very likely NOT match up. That shows that Opacity has been altered in the bad Clips. This can happen all too easily, if one accidentally clicks on that rubberband, when trying to Move a Clip. One should not work too quickly, and make sure that when they click on a Clip, they have Selected the Clip, and not the Opacity (default display) of the Clip. This nails me, when I am going too quickly.
PS - one can also Select the Clip, go to Effects, then Edit Effects, and look at the Opacity setting there.
Bob and Hunt were Johnny On The Spot and fixed my problem immediately. Thanks guys.
Yes, you have to watch those danged "rubberbands." The same thing with the Volume rubberband in Audio Clips. I seem to "grab" them more often, than I should. Just clumsy clicking on my part.
Thanks for letting us know that this fixed the situation and happy editing,