Go to your "tableau de bord" (control panel) and then "modifier votre profil" (modify your profile).
At the bottom, you can select a font for the writing of your messages.
To choose the colour, click on "aide" (help). A window appears with a code corresponding to each available colour.
Once you've selected the colour, enter the code (#......) in the previous page in the corresponding inset.
Then enter the name of the desired font.
You have the choice among:
Arial
Arial Black
Arial Narrow
Book Antiqua
Century Gothic
Comic Sans MS
Fixedsys
Franklin Gothic Medium
Garamond
Georgia
Impact
Lucida Console
Lucida Sans Unicode
Microsoft Sans Serif
Palatino Linotype
System
Tahoma
Times New Roman
Trebuchet MS
Verdana
Then tick the boxes if you wish your text to be bold, underlined or italics. If you don't want, don't tick them.
After that click on "enregistrer les changements" (save your modifications) to make changes valid.
The selected font does not appear when writing, but it will after sending the message.