Using peroxide alone will not give you this result. In order to acheive this on dark hair, you'll need to lighten and then tone. Since you hair is relaxed, I would advise against going blonde unless you hair is in top top condtion (no breakage, no split ends, no shedding) and you'll be able to handle the upkeep between relaxer and haircolor touchups, condtioning and recontructing. Here's a few tips.
1. Wait at least 2 weeks after a relaxer to lighten. PLease be sure tha you hair and scal are in excellent condtion.
2. Only use a liquid lightener along with a 20 volume creme developer. Any higher and you'll just end up mush wet elastic for hair that cannot be repaired and will have to be cut off. I recommend Clairol 7th Stage (found at most BSS and SALLY's) plus 1/2 of the activator packet and 20 volume creme developer.
3. Relaxed/texlaxed hair lightens a lot quicker than natural hair so keep an eye on how light your hair gets. I'd say about 20-25 minutes would be enough. Do a strand test ahead of time to be sure.
4. Do a hardcore protein treatment immediately after lightening and right before coloring/toning. this will help ensure even color all over. After coloring do a deep moisturzing treatment.
5. Now that you hair is double processed, you have to be extra gentle with styling. Use very low or no heat, trim dead ends asap, oil your ends and wrap your hair at night.
Your hair will need weekly protein and moisturzing treatments and a monthly hardcore protein treatment as well.
6. Keep track of your relaxer touch ups and hair lightening touchups. Remember you CAN'T relax bleached hair for it will melt and you CAN'T relax and bleach in the same day or else you'll wind up with severe chemical burns, and run thr risk of permenan hair loss.
ALWAYS wait at least 2 weeks after a relaxer to lighten or do any lifting color. In fact, it would be best to switch to a mild strength relaxer to lessen the damage factor.