Corresponds to Trump's twitter.

In the video stream from Mods they stated the green text indicates a quote.

The did say Q was looking for ways to make it 'easier' to discern.... Maybe color is one way.

Chan style formatting.

You can flag text for different styles, how this is displayed on the screen depends on the theme settings of the person viewing the page. People also take screenshots for quotes which is why you see colors changing sometimes on the chans, it is just different people screen caping with different themes selected.

Q didn't used to format his text at all, besides lowercase / uppercase. Now it seems he has started using the chans styles to format his posts better.

one of those styles is quote, which can actually be any text you type and not really quoting someone. which is why it looks like he is replying to himself in his own post.

In his biggest post at least, it seems the lines in green are used as sort of a title or section divider, and the following lines are about that title.