Now that I see the mother colony, I can see it looks exactly like A. maxima, as described in books.
If it were side by side with this maxima, I wouldn't be able to tell them apart.
Here's another photo of A. maxima
Characters: Colonies are cerioid with corallites up to 50 millimetres diameter. Septa are coarsely toothed. Polyps have a fleshy mantle up to 100 millimetres diameter and with a Lobophylliaâ€"œlike texture.
Colour: Green, grey or brown. Similar species: Symphyllia wilsoni. The fleshy mantles are more extensive than those of any other Acanthastrea. Acanthastrea ishigakiensis has slightly smaller polyps. Habitat: Known only from moderately deep, turbid water. Abundance: Rare.
Source reference: Veron (2000). Taxonomic reference: Sheppard and Salm (1988). Identification guides: Sheppard and Sheppard (1991), Coles (1996), Carpenter et al. (1997).
Notice that in the color description there is no orange, red, or pinks.
Another picture of A. maxima
Scientific Name Acanthastrea maxima
Common Name "Fleshy Artichoke Coral"
Color Dark brown or green.
Distinguishing Characteristics
Like the starry cup coral, heavy septal spines are the dominant characteristic of this species. However, the diameters of its calyces are much larger, up to 5 cm, and polyps may expand to twice this diameter. This species is endemic to Oman, meaning that it has been encountered in only Oman waters, having been described from a specimen first found off Ras al Hamra.
Habitat
Thus far, fleshy artichoke coral is very uncommon and has only been collected from the ridge area lying between Ras al Hamra and Al Fahl Island in the Muscat area, and in the nearshore waters at Sahd, Dhofar. It appears to be favored by relatively low light and high turbidity conditions that are present over sandy bottoms where most other coral species are not abundant.
Info taken from
http://www.bishopmuseum.org/research/pbs/Oman-coral-book/Chap3/CorBkCh3htm.htm
I'm sorry to be the one to tell you that you don't own an Acanthastrea maxima. No one does.