Any smart bulb I've used (and I've tried a lot...) turns back on to its last color and level when you issue an on(), as long as the off() was also issued via software. By this I mean that you didn't use the wall switch or otherwise forcefully cut power to the device. In that case, behavior varies. Many newer ones will turn back on to their last color and level. Many will turn back on to their default settings, usually warm white (around 2700K) at 100%. Hue bulbs with recent firmware on a Bridge network can optionally restore to their last state, even an "off" state. In any case, this particular case is up to the bulb, not Hubitat. I've never seen one that doesn't restore its state if all the on/off actions you use are "soft" and not physical.
So, I guess a few questions are: what bulbs are you using? How are you turning then on and off? Finally, if for some reason your bulbs don't match the above behavior, unless you have a bulb that supports prestaging and you have it enabled (or again have a bulb the doesn't conform to this norm), the setColor or setColorTemperature commands (and their associated actions in Rule Machine, for example) will turn a bulb on (usually directly to those settings; some bulbs may fade from the previous color) if off. The setLevel command will do the same (but again is usually not necessary because most bulbs will remember if turned "soft" off).