matplotlib画scatter图报错：TypeError: ufunc 'sqrt' not supported for the input types, and the inputs

报错如下：
TypeError: ufunc ‘sqrt’ not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ‘‘safe’’
原程序：
plt.scatter(k_point[2][i], k_point[3][i], color[i])
修改：
plt.scatter(k_point[2][i], k_point[3][i], c=color[i])
程序的后面缺少等号（即c=）