Lev7 Firey Arcana (Firey Arcana: At 7th and 16th level the red dragon adds one spell with the fire descriptor of a level he can cast to his list of spells known.)
Lev 8: Locate Object (At 8th level it can use locate object as a SLA 1/day per 4 HD it has.)
Lev 9: Greed (Greed:At 9th level a red dragon can instantly discern the monetary value of any objects in his view. He can also memorize the number and type of each item and notice if anything is missing or added to that group of items with a new glance. )
Lev 10: Fire Lord (Fire Lord:At 10th level a red dragon casts spells with the [Fire] descriptor at +2 caster level and ignores any limit on caster level on such spells.)
Level 11: Arcane Skin (Arcane skin: At 11th level the red dragon gains SR equal to his HD+11.)
Level 12: Iron Scales (Iron Scales: At 12th level the red dragon gains DR/magic equal to half his HD.)
E6 Feats I just made up based on 6+ advancement:
Firey Arcana (Dragon) (E6)
Prerequisite: Red Dragon Class Level 6th
Benefit: Choose a spell with the fire descriptor of a level he can cast to his list of sorcerer spells known.
Locate Object (Dragon)
Prerequisite: Red Dragon Class Level 6
Benefit: Dragon gains Locate Object as a SLA 1/day
Greed (Dragon)
Prerequisite: Red Dragon Class Level 6
Benefit: A red dragon can instantly discern the monetary value of any objects in his view. He can also memorize the number and type of each item and notice if anything is missing or added to that group of items with a new glance.
Fire Lord (Dragon)
Prerequisite: Red Dragon Class Level 6
Benefit: A red dragon casts spells with the [Fire] descriptor at +2 caster level and ignores any limit on caster level on such spells.
Arcane Skin (Dragon)
Prerequisite: Red Dragon Class Level 6
Benefit: Red dragon gains SR 1 as an Extraordinary ability. If Red Dragon already has SR, this feat provides a +1 cumulative to SR, to a maximum of SR 17.
Iron Scales (Dragon)
Prerequisite: Red Dragon Class Level 6
Benefit: Red dragon gains DR 1/magic. May take this feat multiple times. Each time it's taken you add +1 to the DR, to a maximum of DR 5/magic.
And the rest I think might be too powerful for E6. Growth, Crush, Frightful presence, Hellfire, Burn, Revenge, Find the Path, Tail sweep, Discern location