White light is not one color. Some whites look golden, like a candle or an old incandescent bulb. Others look crisp and slightly blue, like midday daylight. Lighting makers describe this with color temperature, measured in kelvins and written with a K.
Lower numbers look warmer. Bulbs around 2700K give the familiar soft, yellowish light most people have in living rooms. Around 3000K is still warm but a little cleaner. By 4000K the light reads as neutral, and around 5000K and up it looks cool and bright. Names like "warm white", "cool white" and "daylight" are not used the same way by every maker, so always ask for the actual K number.
On the outside of a home, warm whites usually look best for everyday use. They flatter brick, stone and painted siding, and they match the porch lights and window glow most homes already have. Cool whites can look clinical against brick at night, though some people like a cooler white on very modern exteriors with dark trim.
A useful test is to stand at the curb at dusk and compare. What looks fine on a sample board in a showroom can look very different against your own siding.
Every addressable light makes color by mixing tiny red, green and blue LEDs. That is RGB. Turn all three on and you get white, but it is a mixed white, and it often looks slightly tinted, a bit blue or a bit pink, depending on the product.
RGBW adds a fourth LED that is white on its own. When you choose a white setting, the light can use that dedicated white LED instead of mixing. The result is a cleaner, more natural white, and on many systems you can set the warmth of that white.
The trade is that RGBW lights have one more LED per pixel. Whether that matters depends on how you plan to use the system. If you expect to run white most nights of the year and color only on holidays, the quality of the white is the thing you will look at most.
Because each pixel can show its own color, you can also blend. A warm white with a touch of amber reads like gaslight. A soft white alternating with a pale gold can feel festive without being loud. For holidays, saturated colors such as a deep red or a true green look strongest when the brightness is turned down a little, since full brightness can wash out color at close range.
Ask whether the system is RGB or RGBW, what color temperature its white LED is, and whether the white can be adjusted warmer or cooler. Then ask to see it lit.