Can it also be solid white

Hello, Dear, This light bar is single white color main LED with halo can't strobe or flash, but it can stay steady solid white. If you want your light bar strobe or flash, you can order our color changing light bar with halo, You can choose the color you want, for example, you only want white. If you choose white/amber, there will be solid/flash white color, solid/flash amber color;  main LED will be controlled by remote controller, halo will be controlled by Bluetooth APP named Magic LED. Please check: https://www.vividlightbars.com/collections/dual-color-strobe-curved-light-bar/products/waterproof-54-curved-led-light-bars

What is the difference between the regular cree and 4d Cree?

Hello, Thanks for your inquiry. They use same led chips, just different in led lens and 4D lens Cree is brighter than regular cree.