Copper chloride color in electrolysis of salty water I tried a simple water electrolysis experiment at home, with $\ce{NaCl}$ as electrolyte, and a $12 \,\rm{V}$ battery.

My wires were made of copper and $\ce{H2}$ bubbles were only forming at negative terminal (cathode). On the positive side (anode), nothing was happening.

After $3$-$4$ minutes, water started to change into a greenish-blue color and I realized that it must be copper reacting with chloride ions. After $15$ minutes, my solution was light blue with exceed $\ce{NaCl}$ at the bottom, after taking the wires out the solution started to turn into a yellow color in about $10$ minutes.

What was the yellow solution and why didn't cathode produce any oxygen?

I'm also worried that the yellow solution might be chlorine because I later boiled the solution.
The color of the solution is probably due to the presence of blue copper(II) ions ($\ce{Cu^2+}$) and greenish tetrachlorocuprate(II) ions ($\ce{[CuCl4]^2-})$.

The change in color comes from the equilibrium

$$\ce{Cu^2+ + 4 Cl- &lt;=&gt; [CuCl4]^2-}$$

Low concentrations of chloride favor the formation of the blue copper ions. High concentrations of chloride favor the formation of the greenish tetrachlorocuprate ions.

If a significant amount of chlorine had been created you should have observed bubbles at the anode and the typical chlorine smell.