Maybe the following passage has something to do with why Douglas Adams decided to make it green. I love this part of the story where he draws a clever analogy between the fiscal policy of the Golgafrinchams and our monetary system - the point being that the paper money has no intrinsic value, and its relative value is very much dependent on many different circumstances, some quite arbitrary and contrived.
'How can you have money,' demanded Ford, 'if none of you actually produces anything? It doesn't grow on trees you know.'
'If you would allow me to continue...'
Ford nodded dejectedly.
'Thank you. Since we decided a few weeks ago to adopt the leaf as legal tender, we have, of course, all become immensely rich.'
Ford stared in disbelief at the crowd who were murmuring appreciatively at this and greedily fingering the wads of leaves with which their track suits were stuffed.
'But we have also,' continued the management consultant, 'run into a small inflation problem on account of the high level of leaf availability, which means that, I gather, the current going rate has something like three deciduous forests buying one ship's peanut.'
Murmurs of alarm came from the crowd. The management consultant waved them down.
'So in order to obviate this problem,' he continued, 'and effectively revalue the leaf, we are about to embark on a massive defoliation campaign, and... er, burn down all the forests. I think you'll all agree that's a sensible move under the circumstances.'
The crowd seemed a little uncertain about this for a second or two until someone pointed out how much this would increase the value of the leaves in their pockets whereupon they let out whoops of delight and gave the management consultant a standing ovation. The accountants amongst them looked forward to a profitable autumn.