Using a box blonde to bleach hair before semi permanent colour?

when u use the box blonde they do have the conditioning properties in them but all u have to do is to reshampoo ur hair again after u have washed it off as this will open the cuticle in ur hair. although only thing is with putting the purple colour over the top it may be too wishy washy. for example if u paint a white wall with a colour it dilutes it a wee bit. so u may need to put the purple on twice to get it to stick as when u bleach ur hair u are removing natural tone and depth so there is nothing left for the colour to stick to.