this thread is in the CSS customization forum and you do not have the CSS editing upgrade. Although the issue seems the same to you it is not. devblog is telling you you ought to have posted your own thread and not posted into this one. I will answer your question.
The colored border is there because you are linking to a larger version of the picture. The colored line appears when you rollover an image which is linked to a larger version, another site, or to an attachment page. You have two options for removal.
(1) To remove the link-border and also to have your image not link to anything,
as you insert new images:
choose “None” on the “link URL” line.
(2) If you want the image to link to something:
Edit your post after you have inserted the image by clicking the image and choosing the mountain icon. Choose “Advanced Settings”
Then on the line “image properties”
type in “0″ (zero)
(You can do this in the HTML editor if you are comfortable with that as well)