I somewhat agree to what pcfriedrich mentioned. Try separating it from the other oscar and feed him well... the colours might become more intense and stable. Since it's already shown you colour 10% time, that means it HAS colour, just that it's reluctant to show in front of the other O.
A bit off track... I once had 2 malawi peacock in the same tank and for 6 months one of them never showed any colour. I thought it to be a bad specimen, until the dominant peacock was killed by a mbuna and it promptly became colourful!
A bit off track... I once had 2 malawi peacock in the same tank and for 6 months one of them never showed any colour. I thought it to be a bad specimen, until the dominant peacock was killed by a mbuna and it promptly became colourful!