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The structural and magnetic properties of the archetype type-II multiferroic RbFe(MoO₄)₂ have been well studied due to interest in the low temperature antiferromagnetic order and its coupling to the induced ferroelectric order. However, little is known about the optical properties of this complex oxide. There have been low energy spectroscopic characterizations, but no reported linear characterization up into the band edge. Here we explore a group of similar such complex oxides: RbFe(MoO₄)₂, RbFe(SO₄)₂, and RbFe(SeO₄)₂. Substitution of the A-site in RbFe(AO₄)₂ can result in comparable, spectrally tunable absorption features that appear below the optical transition band edges. Their absorption spectra show strikingly similar thickness and temperature dependence, despite their different growth conditions and electronic/magnetic properties. We further discuss the potential origin and impact of these tunable optical transition states in the RbFe(AO₄)₂ complex oxide family.