The Union are the Northern States, and The Confederates are the Southern States. As for colors, gray stood for the confederates because the union owned more factories. Leaving the union with the color blue.
They (The Union and Confederates) had fought over Fort Sumter because when the Union had come to the fort, this action provoked and seemed like an insult to the South. This happened on Christmas day as well, not only have they provoked the confederates, but they have stepped onto their land.
This had happened on April 12, 1861, at 4:30 am. This was from when one cannon shot was fired from the confederate side.
The Battle of Fort Sumter was in South Carolina. During the battle, shots fired each other and the confederates continued to fire cannons directly at the fort. Ships had been bombarded by strong winds. Another thing about this battle is that there was a weapon used by the confederates called the "red hot-shots."
The Union was in Confederate Territory because they had taken over the fort, but due to the siege, the union's supplies were running mildly low.
The Union had absolutely no choice but to surrender to the confederates. Because of the surrender, The Confederate side had won the battle of Fort Sumter. After this, shots have broken out continuing The Civil War.