Speaking of corn syrup - - start checking the labels of processed foods and drinks - e.g., sodas.  You'll find "high fructose corn syrup" everywhere!  (fructose literally means "fruit sugar" and of course botanically, corn kernels are individual fruits of the corn plant!  have a good holiday season.

Interesting results - - I assume your corn syrup was diluted - - how much and with what? (pure corn syrup is "thick as molasses"  High concentrations of sugar in any syrup, jam, or jelly is a natural preservative, just like salt in pickles or olives.  This is due to osmosis with the high concentration of solute drawing water out of bacterial cells, killing them, as well as killing the cells being preserved.  THis is probably what happened to your leaf cells in cup 2.  It would be interesting to look at a thin slice of the leaf tissue under a microscope to see if the cells are plasmolysed ( cytoplasm, including chloroplasts, shrink away from the cell wall because the internal vacuoles have lost water).   That could be what's happening to some of the cells in cup 4 too.  Cup 3 is the mystery to me that I would want to investigate further.

So, your initial experiment already used different liquids (plain water and a sodium bicarbonate, baking soda, solution).  I think you had more (faster) results with the bicarbonate, so you will probably want to add the same amount of bicarbonate to whatever solution you use for your follow up expt. 

For different colored lights, you want to be sure that the intensity (brightness) is the same for each of the colors used.  A start is to use the same wattage of lamp, but even here different colored lamps, of the same wattage, will produces different amounts of energy.  If someone has a light meter, that would be great, you just need the same amount of light.  If they are not the same at the start, move one lamp closer (to increase) or farther (to decrease) until they both are the same.  If no one has a meter, see if your parents or someone at school has an old manual, single-lens reflex camera with a built in meter.  Again, all you need is the same intensity.

Different liquids are going to have the same problem - - anything pigmented will absorb light differently.  So, if water is your control, don't use Coke, use a clear soda of some kind instead - -or dissolve something else in water besides the bicarbonate - e.g, salt or sugar.

Light duration is probably the most straight forward.  Just be sure that when your different treatments are in the light, they are right next to each other so all other environmental conditions are identical.

Good luck