How to enable syntax highlighting in ranger preview

I have a transparent terminal that works with ranger's image preview. I use termite (terminal emulator) and compton (compositor) for transparency (a nice combo when you use i3wm).

Here's the result:

The only problems I had were with tmux (images are displayed, but not always at the right position and sometimes the terminal needs to be refreshed).

Note that the text and the image are also transparent since transparency is handled by compton. This only works if you don't add too much transparency, else you need a terminal emulator that handles transparency and works with this feature (I tried with terminator and I did not work for instance, same for urxvt). 85% opacity gives me some transparency and good readability, so this setup works for me.

Update

True transparency is supported once again in termite, but it suffers from the same issues as urxvt when you enable transparency (failed to execute w3mimgdisplay error, cf. @slm's answer).

To be very specific and change the dark blue on black highlighting for PHP scripts in Joe:

In Ubuntu 16.04 and with Joe 4.1-2, edit:

/usr/share/joe/syntax/php.jsf

And change:

=Constant_sq blue

To some other color of your choosing:

=Constant_sq yellow

As mentioned you'll need to edit the appropriate .jsf file for your scripting language of choice, and the affected variable. To fix XML recoloring, edit xml.jsf and change:

=Tag blue

to

=Tag yellow.