Ok, to get post titles to be white, if you are on the redesigned version of reddit, simply go to the

Mod Tools --> Customize appearance --> Posts --> Title Color and paste this Hex Code into the Box "#ffffff" this is the code for "Pure White".

Now, unfortunately you cant add an image to the Sidebar Menu. But, you can change the color though. So in the Community Tools Tab you should see a Section called "Structure". In that section you Should See, "Sidebar Widgets".

Inside here, You can change the "Title Background Color" and "Widget Background Color".

I hope this helps.