Make yellow flame into blue flame in a gas fire place?

First is this a decorative fireplace? if it is yellow is what you want not blue! Often the fake logs have chemicals within them to color the flame.

If this is a furnace/boiler to heat your house then you are correct you don't want too much yellow flame as it is less efficient. You will need to have it cleaned professionally and have them check the flues.

As for Carbon Monoxide (not carbon oxide) you are correct this is not something you want as its deadly! This is where the drafting of your chimney and the piping to it is very important. Make sure you don't have any holes use a smoke gun to test the seams.

For every cubic foot of air that goes up the chimney you need to have a source to replace it within your house. Depending on how tight your house is you may need a air to air heat exchanger to expel bad air and to allow enough fresh air to come in from the outside to feed your fireplace or boiler/furnace. Don't forget about candles or any other burning item you have in the house they too create Carbon Monoxide!

Make sure you have a Carbon Monoxide detector near your fireplace and other locations in your house.