Any healing build that doesn't do it the right way probably will get bored in combat. In-combat healing is generally ineffective anyways- the spells often have touch range, the hp healed is seldom enough, and it removes one player from the action economy of hurting enemies.
Life oracle's life link mitigates that somewhat- you can cast and maintain a life link (or several) at the same time, but some DMs may rule this as "taking ongoing damage while casting".
With your current group, you're going to have a utility/summoning caster, a debuffer, and you- the buffer, preferably. You'll have the ability as an oracle to spam spells that remove conditions, heal party members when needed, and throw around your own stuff when none of that is needed. Your current build (color spray spam) is nice for what it's intended to do, but I wouldn't put all of my eggs into one basket. Color spray is is a mind-affecting illusion with a short range and a limiting area of effect (cone which will catch party members just as often as not). If something's not immune or too high HD to be significantly affected, you might still hit a party member. Other Spell Perfection builds focus on being able to mitigate this or circumvent danger- see the infamous Dazing fireballer with the admixture subschool, which adds crowd control, damage, and choice of element to one spell. There's nothing worse as someone who focuses on Color Spray than running into one of many enemies that are immune to its effects.
You may be better off focusing on other spells (or not taking Spell Perfection) and instead using things like Rainbow Pattern to lead enemies away or similar buffs and helpful effects. All of this is not to say that a color sprayer can't be useful- it'll just require more magical doodads to be useful all of the time.
While it's not optimal, the heavens oracle also gets some good blasty spells. Chain lightning and summoners get along very well, and sunburst is an amazing AoE blinding effect. No matter what you focus on, you're still a 9-level caster in the end. It's hard to truly go wrong.
With a Inquisitor, Paladin and a witch in the party you should be fairly well covered for healing.
Paladins have access to restoration and a fair number of other condition removal spells. They also get mercies that can be used to cover things not on their spell list. The nice thing about mercies is that when a paladin uses lay on hands the target gets the benefit from all the mercies the paladin has.
The witch has both raise dead and resurrection on her spell list so should be able to deal with bringing characters back to life. She also has Heal which will take care of almost all other conditions except negative levels or permanent ability damage, but the paladin as I mentioned does get restoration so can deal with those.
The inquisitor also has a lot of these spells on his spell list. He may not have them as spells know but they are on his list. He does not have spells to raise the dead, but he does have both heal and restoration on his list. The smart thing to do is to get a couple of scrolls with these spells so if one of the other casters are incapacitated he can use a scrolls to bring get them up.
This means that if you play an oracle you don’t need to use all your spells for healing. As an oracle you will get all of the cure spells automatically without having to cut into your spells know. Take the blackened curse to get some blasting spells. Work with the other party members to balance out the rest of the healing. Chose a decent number of offensive spells as well as the basic buff spells the wizard does not have.
Your understanding of heightened spell is wrong. What heightened spell does is allow the spell to be cast in a higher level slot and count as a higher level spell. So in order for it to be counted as a 9th level spell you need to use a 9th level slot. You can use any slot as long as it is higher than the level of the spell. So if you used a 5th level slot to cast color spray it would be considered a 5th level spell . Usually you use heightened spell to increase the DC of the save, or to allow it to bypass defenses that only work on a lower level spell. For example if you used a 4th level slot for color spray it would ignore a lesser globe of invulnerability and the DC for the save would be 3 higher.