Yes, it's fine to apply permanent color over semi permanent.
If the scalp is in good condition and was not irritated by the semi permanent color, it's OK to apply permanent color within 24 hours after initial color service.
Yes, it is OK and safe to apply semi permanent hair color on top of semi permanent hair color. The end result may be a little darker though.
Yes, you can apply permanent hair color on top of semi-permanent hair color. Make sure that you do a deep conditioning treatment or hair masque before and after you color your hair.
Yes you can. Highlight is a term for lightening the hair so you will have to use a lightning product to achieve the best results as permanent color will not lift the semi permanent color to the right level, but be sure to read the instructions and apply properly.
yes, but semi-permanent colors will not lift you natural hair color, and if it you put a lighter color over a darker color it will not do much other than give shine
You can but there is a chance that it can alter the results because of the semi permanent color. I would wait until it washes out before adding more.
yes it your applying a coloour to blonde it may fade but still remain
It is recommended that you wait 4-8 weeks between color treatments because the chemicals can damage your hair and you need to give your hair time to restore itself. You can apply the semi permanent hair color a couple weeks later, but make sure to condition your hair well and check with your stylist before taking that risk.
Semi permanent colour will wash out in 6-8 weeks.
The permanent color should cover the semi permanent one, if dark enough. But, yes, eventually the semi permanent color will fade away.