Partial answer ; changing colours without actually changing the layout, yes, can be done.
Since you are not familiar with it : alternate method to get the 'grasp'.
Use Firefox browser, use Firebug addon and/or webdeveloper.
Visit your page, right click (when addons are installed in FF) choose check element with Firebug. It will display a lot of info. Colours etc..c can be found on RIGHT side of window (different css files in use).
On left click and see what you are 'selécting' and see on right which is triggered.
Suppose you now know that superhero css (line 9 etc..) is used click on it, and see what happens. This is merely a description to get you started, and with FF now in this mode you can see (live) what happens. It does NOT save it !!!.
The actual files to be changed (backup always) are in the system theme files..
You are given pointers to which one that should be.
1 small example : background is blueish/greyish This color is in the body, created in superhero css line 9 (back..color.. 2a333c #click it) Change that to RED
do that as described in FF with firebug and see what happens..and jusr remember what file and what position ( for all involved).
As for q2 (please keep questions apart) no troubles on Android I can get easily to sign up (button top right is mini link to 'header' .