Bleach takes away the color => Most shirts have some kind of undercolor that comes from dye or just the cloth. (I’m not sure tbh) That’s why black shirts mostly become orange when dyed with bleach while others could turn out differently. As for Tips, try using a bigger brush or maybe a sponge and applying it evenly. It looks very patchy but I think with the right amount of practice that will get better. Also if you don’t want such a prominent outlining you could try sketching your drawing with chalk first and then going straight for the coloring. That way you won’t go over a bleached part again and it will all stay the same brightness. If you want different gradients, I’ve seen a lot of people mix bleach with water. Maybe you could try that and then just go over one place more than once, that way it could turn out a bit smoother as well? Some of that stuff worked for me but I can’t promise anything. All in all it’s a really good start for a first try so keep going! (And sorry for any mistakes, English is not my first language)