My girlfriend and I are both pretty nerdy, she is a math teacher and I am an engineering student, and we have decided to get married.  In most of the weddings we have been to there is usually some symbolic display of unity during the ceremony, 2 candles lighting another candle, pouring 2 different colored sands together into one container, and the list goes on. So to celebrate our geeky union and to do something completely different from anything else we have seen before, we wanted to create a chemical reaction during ceremony.  Here are the stipulations:

1.  The initial reactants should be clear and colorless (resembling water)
2.  Both initial reactants should be easy to obtain
3.  Both initial reactants and final product should be "safe".  (Nothing too toxic)
4.  We are hoping for either a drastic vivid color change or the release of a visible non-toxic gas (smoke)
5.  The less mess the better
6.  The less heat the better

Basically, I am shooting for something simple like a vinegar and baking soda solution reaction without the mess.

Any suggestions?

Thanks,
Don

Both of which are safe and easily obtained (in chemistry sets or science stores). Description: EXTREMELY vivid color change. Awesome to watch.

NaOH/phenolphthalein

NaOH is cautic soda
will a very dilute solution give good color?

NaOH is cautic soda
will a very dilute solution give good color?

Good question, but it shouldn't be a problem.

http://www.ph-meter.info/pH-measurements-indicators

For pH=10 color change is complete, pH=10 is 10^-4M, hardly concentrated enough to be dangerous.

Note: I have edited your post to show quotes properly. Use square brackets [, not <

Yeah, phenolphthalien and NaOH would be pretty cool.  What an awesome idea, I am so doing that at my wedding.  Fitting for a chemist

The luminol reaction can be bright enough to see in daylight, provided that the altar doesn't have a large window as a backdrop or something.  It depends on the concentration, too.  I think that hydrogen peroxide gives a blue glow for a few minutes while the bleach gives a green-yellow color.  I've heard of other colors being produced with different oxidizing agents, too.  Of course, if this is done in low light or in a dark room, the effect will be spectacular.

As for my wedding, assuming that I'm ever going to be married, I'm going to shoot off a heart shaped red firework followed by two golden interlocking rings.

In general every indicator listed at http://www.ph-meter.info/pH-measurements-indicators as colorless on one side will do

It can only make a wedding more memorable