I've read the posts about why Green Tea can appear brown, and it makes perfect sense.    However, what I'm experiencing is different.  When I reuse my Green Tea Bags a second time, I get the green color one would expect.  Totally counter intuitive, I know.  Any ideas why this is happening?  Some additional information: The green tea bags I buy are from a local Asian Market.  They are sourced from China, so not likely high quality.  I also do NOT place them in boiled water, but place 8 bags at a time in a gallon pitcher, in the room temperature purified water (reverse osmosis water), and let them steep for 24 hours.  I then refrigerate the tea.  First batch is always brown but the second batch made from the re-used bags is green. 
When you brew tea, you extract certain chemicals from the leaves which is what gives flavour and colour to the water that you then drink and (hopefully) enjoy. Because there are a number of different compounds involved, they extract from the tea leaves at different rates.  When you brew a second cup, there won't be as many of the fast-extracting compounds in it because most of those went straight into the first cup. Thus the second cup will not have the same colour or flavour as the first.  A third cup will proceed along similar lines, as the balance of compounds extracted from the leaves changes yet again. Likewise for fourth etc. until the leaves can no longer produce enough flavour to make another cup worth drinking (this varies according to your leaves, brewing method and personal taste - I've got some teas which will happily do four brews, while others give a very poor third cup that I'm seldom in the mood for).  So the reason why the second cup is different is because brewing the first cup changed the composition of the tea leaves. 