Joomla fade background from white to black on first load - joomla

Question

Currently I'm working on a black background joomla website. In template 'index.php' < head > i have < style type="text/css">html, body { background-color: #000000; } </style> & this changes the background to black & ensures no flashes to white on page refresh etc., but the initial change from white to black is very sudden.
I'm looking for an simple, elegant solution that on first load fades the background color from white to black, thereafter background remains black.
To achieve this I've used the following in the 'index.php' found in Joomla root (not the template index.php) - I place it before the php in that file - effect looks cool and works fine :
< html >< head >< style type="text/css">html, body {background-color: black;-webkit-animation-name: backcolor;-webkit-animation-duration: 6s;animation-name: backcolor;animation-duration: 6s;
}
#-webkit-keyframes backcolor {
from {background-color: white;}
to {background-color: black;}
}
#keyframes backcolor {
from {background-color: white;}
to {background-color: black;}
}
}
< / style >< / head >< body >< / body >< / html >
... starts the fade in then runs joomla php, page builds as fade progresses etc. - all good.
But, of course, with every page request the includes 'index.php' in the URL it switches the background back to white then runs the fade in to black again.
So I've been think about how to use the existence / or not of the Joomla session cookie as a simple way of determining whether or not to run the fade in.
The idea is that on first load the root 'index.php' file won't yet have have created and set the session cookie.
So if I could then cook up some sort of php 'if' statement to place at the very top of that root 'index.php' file like " 'get session cookie' -> No session cookie : Run the fade in -> if there is a session cookie : Don't run the fade in ".
Could this work ? Any ideas on how to code this or any other simple alternative approach to the problem would be appreciated.
Cheers PaulZero