What are the differences between White Umberalla and Silver Umberalla?
White umbrellas are usually used when you want to light a whole room or to get a really soft shadow on the model (by position it close to the model). This will give you a glow appearence similar to the classic window light where you position the model next to a large window.

Silver umbrellas are for when you want to bounce more light back to the subject with slightly more define shadow. It will also give you a slightly more highlight and glow on the model skin. They will have a silver shine on them, similarly the gold one gives you a golden look, warmer tone on the skin. Another point is that with silver reflective, you will have less light spill than the white shoot through. And because of that u get vignette in your photo with darker frame around the edges if you zoom out far enough.
What are the differences between Continous light and Flash light on umberalla? Any different in pic result? or just save power that’s why we use flash.

Flash (Strobe) pumps out a lot more power in shorter burst, if you need to freeze something then you will need to use the flash. They are usually colder (blue/white) in colour temperature, similar to natural day light.
Continous light uses a lot of power to stay lid. These are usually tungston with orange/yellow (warmer), sunset appearance popular with fine art nude. And because the light stay on all the time, you can work out the shadow very quickly and adjust it accordingly. Hence most of the studio flash unit have modelling light to show you what the shadow might look like once the flash is fire. Modelling light can be use as continuous light but sometime are just not strong enough.