There is some scary advice on this thread. I wanted to share some basic info with all of you on at-home color. I went to hair school years ago and have done my own hair (cuts when it was short and color now that its not). I have destroyed and totall reconditioned my hair several times and have had every color under the rainbow(black, platinum, blue, red, purple, brown, etc., etc.)
1. Find your base level. What are you working with? "Dirty blonde" denotes nothing. Find where you fall on this universal chart
Hair Coloring Chemistry . I have red hair and am usually a 6 to a 6.5 (yes there are degrees on this chart). Note, too that when you make your hair lighter, certain "tones" will come out-- commonly called brassiness-- which can be difficult to cover or change.
2. Figure out if you need to remove or add color. If you want to go darker, you are best off using a "deposit only" color like a semi or demi permanent-- these only "pack" your hair with color and will not "lift". They will never make your hair lighter. Over time, a darker color will build up on the hair and may weigh fine hair down.
If you want to highlight, you will indeed be "lifting" color. To lift more than 2 shades on our handy chart, you will probably want to have help (professional help). You can tell what level you are at by looking on your color box (8.5 will be a blonde, 10 will be a max blonde, etc.) "Lift" also involves the use of developer. A 40 volume developer will give you 2x the lift of a 20 volume which is the standard found in most boxed hair colors. You can get up to 100 volume (pure) developr but only if you are a licensed stylist. 40 volume will generally dry out most hair.
3. If you are lifting, expect an orange stage when going more than 2 shades. You may have to do multiple processes to get what you want and your hair will dry each time. If you want to go from a dark color to a much lighter color, you may have to lose length or do this over several weeks.
The longer you leave the bleach on the more it will lift until it gets to a point where it can't pull any more pigment out of the hair. This means either try again with a new batch of bleach after washing or stop (probably best unless you want very texturized platinum hair which you plan on wearing short).
4. Highlights-- foils give you a chunky or stripey look, balyage is hairpainting, which, when done correctly, can be very dramatic (ombre) or very natural (sunkissed). When highlights grow out, you will need to either redo them or tone your hair a slightly darker color (remember-- deposit only, semi or demi permanent) if you want to get back to your original state.
5. Never used Color OOps unless you have virgin hair that has been dyed darker ONCE.
6. Red fades the fastest but is the hardest to cover. Expect to get a color depositing conditionER (Aveda maybe) if you want to keep your color bright or expect to redo with a semi or demi permanent red every two weeks.
7. Tones-- ashy means green or violet or a combination thereof. Copper means red and orange. Golden means yellow and orange. Burgundy means violet or blue and red. Brown in any color will decrease intensity (Radiant red brown, for example), and may be a decent choice for those not looking to go too bright. Golden will increase intensity and brassiness (Golden Copper Blonde) so its a safe bet you will get some orange tones.
8. Cuts-- fine hair will need a different cutting technique than coarse hair. As a general rule, fine or thin hair looks best between the middle of the cheek and just above the shoulder. Coarse hair can take on a lot of long, razored cuts and as long as its cared for, will look good. But of course there are exceptions. If you have fine, medium to dark hair (level 5 and below) it is not advisable to go platinum blonde ( I did and it looked great until my hear literally broke off). If you have coarse medium to dark hair, you can try but you will get a brassy orange unless multiple processes are used.
With coarse hair, avoid cuts that are all one length unless you are looking for a boxy, dramatic look. With fine hair, avoid excessive layers unless your hair is very short. Some layers are great, but too many will leave you looking like you don't have any hair.
9. Don't be afraid to experiment but be prepared for the consequences. If you love your long hair but want to highlight the heck out of it, be prepared to lose a few inches if it goes awry. Have a backup plan if things don't turn out the way you want.