The slippery definitions of sanity are at the centre of Joe Penhall’s audacious play, Blue/Orange. The piece premiered at the National Theatre in 2000, with an all-male cast including British titans Chiwetel Ejiofor and Bill Nighy.

The production currently on at the Arcola Theatre, East London features an all-female line up, a device through which director Femi Elufowoju Jr. hopes to challenge the idea of certain traits being considered typically male or female.

The hitherto relatively harmonious working relationship of two psychiatrists, Dr Hilary (Helen Schlesinger) and her subordinate Dr Emily (Esther Hall aka the mum in the BT ad campaign) is thrown into disarray when they are confronted with the case of Juliet (Ayesha Antoine), a young woman of African origin who claims that oranges are blue and that she is the daughter of former Ugandan dictator Idi Amin Dada and a Congolese émigré.

Emily believes Juliet shows schizophrenic tendencies and needs to be institutionalised immediately. Hilary however, slightly jaded by several years of practice and caught up in her own pomposity, thinks her junior colleague is overreacting. There is, after all, the slim chance that Juliet could be telling the truth about her background. What’s more, the older doctor is convinced that Emily’s diagnosis has more to do with cultural insensitivity than any real ailment on the patient’s part.

Unbeknownst to Hilary, some of her supposedly noble reasons for distancing herself from ‘ethnocentric’ diagnoses are just as influenced by the paternally racist mindset of which she accuses Emily. Juliet finds herself caught in the middle of the ideological tussle and power play going on between the two colleagues; Dr Hilary facetious and self-important, Dr Emily too easily rising to the bait and undone by ambition. In the professional chaos that ensues it’s not certain whether Juliet’s mental well-being is a priority or merely a bargaining tool in the medics’ game of one-upmanship.

ULTZ’ minimalist box-like set design, as usual, is the silent star of the show. Inside, amidst sterile white walls and cream-coloured furniture are one or two sly concessions to the play’s title; a bowl of juicy-looking oranges and the pale blue of a water cooler bottle in the centre of the room. Outside, the audience sits detached; viewing everything through large oblong slits cut into the externally black walls of the set, lending the scene a cinematic, ‘letterbox’ appeal.

The pace of this production, at least in the first half, sometimes trails behind Penhall’s razor-sharp script. As fine an actor as she is, Schlesinger’s portrayal of Hilary occasionally lacks variation. The volume and tone in which she delivers some of her lines are more suitable to a long diatribe than a very important discourse on what exactly constitutes sound mental health; Elufowoju could have opted for more subtlety.

That’s not to say this is fatal to the appreciation of Blue/Orange. Despite the histrionics the casting is spot-on and there are worthy performances given by all.

Ayesha Antoine’s Juliet is especially nuanced. She deftly balances the character’s assertiveness with a certain vulnerability. You’re sometimes left wondering how much Juliet is wise to the doctors’ game. Does she genuinely believe all her apparently deluded statements or is she merely playing up to the stereotypes surrounding people of African descent and mental illness?

Blue/Orange has the nerve to take on a tricky issue in a non-derivative way and provokes a riveting dialectic in the process. There’s much on which the audience can cogitate; the fine line between hasty diagnosis and self-fulfilling prophecy for instance, or the impact isolation and cultural detachment potentially have on psychological health. Elufowoju’s use of an all-female cast is inspired; an added stimulus to an already fascinating conversation piece.

Blue/Orange is at the Arcola Theatre until 20 November. For ticket information visit www.arcolatheatre.com or call 0207 503 1646.