Change colour of cell after a number of calender days passes

Hi Everyone
Just a slight variation on this formula is needed . Please help.
I have used the formula =and(a1<>"",$a$1+21<today()) which works great.
What I now need to do is expand on that .
I use this formula and format the cell to change to RED after 21 days have been past. I now need that same cell to change to GREEN after 35 days. And then to PURPLE after 42 days.
I have tried adding =and(a1<>"",$a$1+35<today()) and =and(a1<>"",$a$1+42<today()) , but this does not work as it only uses the 21 day formula .
Please explain what I am doing wrong

Onesock

Hi Fotis

Thanks for the reply.
I cant seem to get it right . Please have a look at the attachment and explain where I am going wrong.
Thanks

Onesock