very slight updates to the design

In yesterday's hub meeting the observation came up that almost no one had yet really noticed that the howto contained anything else / was updated since last year, so someone suggested we change the design of the website. Since we don't have a design yet, this just slightly tweaks the colours to some that occurred in the announcement blog post.

@psy macht das sinn? oder kommt das "richtige" design eh morgen raus?