If there was no God we would not have an objective standard to tell the difference between red and blue. Who would determine what is red and what is blue if there was no God? It would be chaos! Anything would go. The colors would be whatever someone says they are. Really, who are we to say what the colors are? Thank goodness we have God to tell us the difference between red and blue . . .
If the above statement sounds completely moronic to you that's because it is. And substituting the words "red and blue" with the words "good and bad" makes the above paragraph no less stupid. There are real metrics we use to distinguish colors. Likewise, there are real metrics we use to distinguish good actions from bad actions. For colors its the wavelength of light. For morality its the well being of sentient creatures. Things that cause harm are bad. Things that promote happiness and well being are good.
The ultimate standard of truth is NOT a God. The ultimate standard of truth is reality.