First off if you have dark hair you need to have a PROFESSIONAL bleach your hair. I have very dark hair and it took a few times for my hairdresser to get my hair light enough (this was before olaplex). Don't let your friend who is good at doing hair bleach your hair. Just don't. As for the color there are many options out there right now but I am going to tell you about two products you can purchase yourself rather then products you have to be a professional to buy. The first product is a semi-perm hair dye that I love and that you can purchase online from a brand called Arctic Fox. Arctic Fox is gluten free, cruelty free and a percentage of their sales goes to helping animals. The color selection and color combos are the best I have seen and they just keep coming out with more, plus you can mix them together or dilute them with their white color (Arctic Mist) and get your own custom color. Another great thing about their color line is it does not transfer. Which if you have ever had a funky color in your hair you will know is huge! I have lost so many pillowcases to hair color in the past. Did I mention all their colors smell like a grape candy? When you receive it in the mail you are going to think someone sent you a yummy treat. Right now I am using a small amount of Purple Rain and Virgin Pink with a lot of Arctic Mist because the colors are ao pigmented that just adding a small amount to the white gives me the pastel shade I am looking for. If I want it to be more purple I add more. It's best to add a little at a time and mix it up to see what color you get because the color in the bowl is going to be the color of your hair as long as you have your hair bleached to a light enough blonde. The color is not damaging at all so you don't have to worry about using color right after bleaching.
Another product that has saved me from having to touch up my color all the time is from oVertone. Overtone is a line of conditioners that deposit color to your hair and actually let you rinse with warm water! In the past I have just added a small amount of color to my regular conditioner and rinsed with cold water to help maintain my color but I don't think it really did anything but these conditioners are no joke. They have deep weekly hair conditioners and everyday conditioners in many shades my favorite obviously being pastel purple. I would want to use these conditioners even if they didn't do a thing for my color because they really work well and make your hair feel and look healthy but the fact that they DO make such a difference and let me keep my hair color from fading makes them a must have for me.