Strong correlation of link gains over multiple wavelengths has been demonstrated in non-line-of-sight optical wireless scattering communication. In this paper, we further demonstrate the strong correlation of the channel impulse responses for different wavelengths. A novel channel estimation method is proposed based on such correlation, where only certain reference wavelengths are assigned with pilot signals. On each channel assigned by the pilot signal, we adopt an improved least-squares method to estimate the channel tap coefficients and the tap length. The channel tap coefficients for other wavelengths can be estimated based on the inter-wavelength correlation. Under the proposed channel estimation, the channel estimation accuracy can be improved as shown by the simulations. We further propose an optimization method for the correlation-based channel estimation pilot pattern based on the receiver channel state feedback. Simulation results show that optimized pilot pattern can achieve significant performance gain over the fixed pilot pattern. Moreover, the channel estimation performance is insensitive to the channel state feedback frequency.