When you click on 'Reply', the original email should be displayed either above or below (depending upon your Account Setting preference) where you would type your comment.

suggest you type something like ' see comments marked in original email', then move cursor to where you want to insert your comment and type.

Note: if they have written the original email using formatted coding then this will effect the font etc. However, you can highlight your section and choose another eg: colour from the Formatting Bar. Alternative option: Copy paste a section and type comments per that specific comment.

Thank you Toad Hall for your reply, however your suggestion is the one that takes a lot of time as opposed to just clicking on the part of the original email, insert my initials, and then adding the text in a different color.

Having the user go back to the inserted text, highlight the text, change the color, is just a real time sink.

ok, Toad Hall - I appreciate your reply.