As mentioned, they are relentlessly green because they're in a wonderful situation where it saves them a lot of money.
The green washing aspects would be carbon offsets and such because those are still up for debate as to whether they really have any positive net effect.
Edit: Got a downvote so I thought I'd clarify. Carbon offsets are the act of paying for carbon neutrality. No matter how efficient or environmentally friendly Google is, they can't possibly be carbon neutral with all their energy use unless they use primarily nuclear power with some hydro, solar and wind built in. Therefore they buy carbon offsets, http://en.wikipedia.org/wiki/Carbon_offset, which allow them to advertise that they're carbon neutral. The controversy over them stems from the fact that they're very similar to indulgences from the catholic church in the time of Martin Luther; paying for greenness isn't actually being green.
I saw a talk recently about how much solar and wind power Google buys, and it's not at all cost effective. Google does it because they think it's cool, not because it saves them money. (But, the rate of return on the investment into wind infrastructure tends to be pretty good; wind power can be sold at a higher price than regular power.)
As an example, look at the Googleplex in Maps some time; all the parking spaces are covered with solar cells to charge the specially-converted fleet of plug-in-hybrids available for employees to borrow during the day. Building solar cells and custom-modding cars to give to employees for free is not exactly "saving them a lot of money". But it sure is cool.
It's definitely cool and if it makes employees happy then it's definitely worth the investment.
I have a personal bias to get over which is that I only believe in investing in energy solutions that can solve large percentages of the energy gap for everyone and not just the ones able to spend the money or work the incentives system.
Google is one of the top few investors in solar/wind power generation projects in the US, not just buying watts, and it is for profit/savings, not a donation.
Could you explain your calculations on that? How is building new infrastructure with brand new technology cheaper than plugging into the existing infrastructure?
