Mussaenda glabra Vahl, Symb. Bot. 3: 38 1794. (Syn: Mussaenda andersonii S.K.Basu & T.K.Paul; Mussaenda mastersii King ex A.M.Cowan & Cowan; Mussaenda penangensis Miq.);
Sikkim to Malaya, Jawa: Assam, Bangladesh, East Himalaya, Jawa, Malaya, Myanmar, Thailand, Vietnam as per POWO;
Common name: Hairless Mussaenda • Adi: Takdeng • Kannada: ಬೆಳ್ಳೋತಿ Belloti • Mizo: Va-kep

White Mussaenda with Orange flowers:
White Mussaenda with Orange flowers
The Orange petals of this plant is narrower when compared  with that of  Mussaenda phillipica.
Date/Time : 20 Jul 2010, 10.44AM
Location- Place, altitude and GPS: Miao, Arunachal pradesh
Habitat- garden/ urban/wild/type: Wild, forest path,
Plant Habit-tree/shrub/climber/herb:  Shrub,
Height/length: Plant height –2-3 feet
Leaves-type/shape/size: /Green leaves – 15-20 cms/Acuminate/ Opposite ?
Orange flower, size –Approx. 1.5cms , green buds

I think Mussaenda roxburghii Hook. f.

Mussanda philippica is a very common introduced species to India. The plant in the picture doesnt looks like M. philippica as the petals are narrow and pointed, whereas, in M.philippica, the petals are shorter but broader and the bract has many color variations. It neither looks like M.roxburghii as it doesnt have the persistent calyx (the key character of M. roxburghii).
I will certainly look in to this later and try id the same. if … can send us a picture of flower in which the calyx is highlighted or clearly visible that would of great help to id it correctly. Please add a picture with leaf too as it is an inevitable part that carry lots of key characters.

Mussaenda for sure, if it was ornamental I would have thought it to be Mussaenda luteola or it may be an escape too.

This appears to be Mussaenda wallichii as per FOIPOWO specimen

After going through detailed description in FBI from IBIS Flora, I feel it more closer to Mussaenda glabra as per FBI description rather than Mussaenda wallichii (which also does not have distribution in Arunachal)