Changing font color on price

Where can I change the red font color to white?

You can go in the config under the tab display and edit the hikashop CSS file.
There you will find the code:
span.hikashop_product_price{
color:#990000;
white-space:nowrap;
}
You can change the color code to #FFFFFF to have it white.

That also changes the listings price, how can I make it so it shows black on the listings but white in the cart?

You will need to use 2 CSS definitions:

.hikashop_category_information span.hikashop_product_price{
color:#990000;
}

.hikashop_cart span.hikashop_product_price{
color:#FFFFFF;
}