= Polychromatic single-slit diffraction
For mutually incoherent <wavelengths>, <intensities> add rather than <amplitudes>: $I(\theta)=\int S(\lambda)\operatorname{sinc}^2[\pi a\sin\theta/\lambda]d\lambda$, where $\operatorname{sinc}q=\sin q/q$ and S includes source strength and detector response. All <wavelengths> share the central maximum but their minima occur at different angles. A smooth white spectrum therefore has a white centre, wavelength-dependent edge colours, no common first dark minimum and increasingly overlapped, low-contrast outer fringes. A particular hue needs the actual spectrum and colour response.
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