Tails Chao???????????

This will work hatch: a normal chao and give it purple chaos drives as Tails. Do this until it looks like Tails. i also have a way 2 make a hyper tails you can: hatch a shiny orange chao, and give it purple chaos drives, and make it take phoenix wings. Do this until it looks like Hyper Tails.

Try getting a yellow egg from the store.

well u could try expirimenting around (by mating different chao) and try to make an orange one or you can just buy a yellow one

Buying a yellow chao egg does not affect how his mouth is supposed to be (white) Try raising him as a fly with Tails.

You can get an official tails chao from phantasy star online episode 1 & 2

If tou want an actual Tails Chao (Legit), Try Phantasy Star online episode I and II. (This requires a GBA And a GBA Link Cable and this only works for the GameCube version) Do the mission : The fake in yellow. Finish the mission, but do not collect the reward. Stare somewhere for a few seconds and a chao will be seen. It will store your data in the tiny chao garden. Find a Chao Transporter and send the data to the tiny chao garden and after you done that, you may collect your reward. You can send it to either Sonic Adventure DX or Sonic Adventure 2 : Battle. Congratulations! You officially have a Tails Chao without any cheats! One more thing, If you didn't know, Tails Chao Functions like Chaos Chao. They're Immortal and they cannot absorb any Animal Parts.

I'll try to break this answer up for ease of use.
1. Tails Chao is sadly not obtainable through evolution. It is a special character chao, and is the only character chao that can be obtained through normal copies of the game, but it requires Phantasy Star online.

2. Provided it appears in the Blac Market, after collecting a number of emblems, Yellow Eggs will occasionally be available for purchase. The closest to Tails chao visibly would probably be a Neutral/Flying Chao, as it looks a bit like NiGHTS.

3.The chao that change colors as it ages is called a Normal Chao(on the color charts at least). It will always stay blue if it evolves into a Neutral chao, turns black if it turns into a Dark Chao, or White if it turns into a Hero Chao. The only variations here are the highlights it has, which are influenced by the Skill type it evolves into.

4. You can breed a Normal chao with Chaos of other colors to create a two-toned Chao of that color. They'll have the Colored chao as their primary color, and a specific color as their highlights. You can take this even further by breeding a Two-Toned Chao with a Shiny chao or a Jewel chao and make a Shiny/Jeweled-Two Tone chao.
Note that on any HD rereleases of Adventure 2, the texture on Two-toned Chao will be incorrectly colored, Shiny Two-toned chao will appear insanely bright, and Jewel Two-toned chao with be invisible, because they didn't put much thought into porting a port of a port lol

Hope this helps in any way, even if it's a year late. Good luck in your chao raising!