# Short answer
It's a bug.

# Full answer
It looks like the "correct" visualisation is the one on the left, where the **bold font** are **not** rendered. For what I could understand ([here](https://github.com/seebi/dircolors-solarized#bold-settings) is the reference) the bold attribute was used, originally, to set the *highlighted* version of the 8 base colours.

> *Historically, there has been a one-to-one correspondence between the bolded versions of the 8 default ANSI colors and the bright versions of the 8 default colors. Back in the day, when a color program demanded the display of bold text, it was probably just easier for terminal emulators to display a brighter version of whatever color the text was (and expect the user to interpret that as bold) than to display a typeface with a bold weight.*

Basically, what is happening here is that, in order to use the full *Solarized* palette, with the *orange*, *purple* and all the levels of *grey*, the colours are called with the *bold attribute*, which in turn refers to the *alternative* 8 colours of the ANSI palette.

*Terminal* understands this correctly, and shows the *orange* and the *comment grey* in *normal* typesetting, whereas *tmux* adds an unnecessary *bold* font to them. In conclusion, the right side is correct whereas the right one is not.

# Question 2
Is there a way to *disable* the bold rendering of *tmux*?  
I still have to do some research about it, and I will update this answer as soon as I find something.

# Answer 2
And here we have the solution! :)

In order to have *tmux* behave correctly we have to call it telling him that we are in a 256 colours enabled environment.

    TERM=xterm-256color /usr/bin/tmux

For convenience we could `alias` this (i.e. you add `alias tmux="<the line above>"` to your `~/.bashrc`).

![tmux interprets correctly the non-bold "bold-alternative" colours][1]

Calling `tmux` as `tmux -2`, for forcing *tmux* to run with 256 colours support (instead of redefining the `TERM` environmental variable) will not allow for correct interpretation of the "bold-alternative" 8 colours (i.e. the brighter variant will also result having a bold typesetting). Therefore, I highly recommend to use the solution here above for having **both** correct 256 colours interpretation **and** non-bold "bold-alternative" colours.

  [1]: http://i.stack.imgur.com/D79sk.png