From what i've seen top right seems to be the most common placement for the add new button, with the exception for middle eastern region where they read from right to left.
Should you save the button at the top or bottom?
Considering that your users will typically navigate to one category, make a change, then click Save Changes, I think placing the button at the bottom/left is best. If your users were frequently making changes across multiple categories, then you'd have a good argument for placing the button at the top.
What should be the color of add button?
What's the best color for Add to Cart/Buy button? The results. As we see, red is the most popular button color among the reviewed websites. Green, blue and orange are very close, altogether making around 74% of the total.