TranslucentTaskBar.cs

using System;
using System.Runtime.InteropServices;

namespace TranslucentTB
{
    class Program
    {
        [DllImport("user32.dll")]
        internal static extern IntPtr SetWindowCompositionAttribute(IntPtr hwnd, ref WindowCompositionAttributeData data);
        [DllImport("user32.dll")]
        internal static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

        [StructLayout(LayoutKind.Sequential)]
        internal struct WindowCompositionAttributeData
        {
            public WindowCompositionAttribute Attribute;
            public IntPtr Data;
            public int SizeOfData;
        }

        internal enum WindowCompositionAttribute
        {
            WCA_ACCENT_POLICY = 19
        }

        internal enum AccentState
        {
            ACCENT_DISABLED = 0,
            ACCENT_ENABLE_GRADIENT = 1,
            ACCENT_ENABLE_TRANSPARENTGRADIENT = 2,
            ACCENT_ENABLE_BLURBEHIND = 3,
            ACCENT_INVALID_STATE = 4
        }

        [StructLayout(LayoutKind.Sequential)]
        internal struct AccentPolicy
        {
            public AccentState AccentState;
            public int AccentFlags;
            public int GradientColor;
            public int AnimationId;
        }

        static void Main(string[] args)
        {
            AccentPolicy accentPolicy = new AccentPolicy();
            accentPolicy.AccentState = AccentState.ACCENT_ENABLE_BLURBEHIND;
            accentPolicy.AccentFlags = 0;
            accentPolicy.GradientColor = 0;
            accentPolicy.AnimationId = 0;

            IntPtr accentPtr = Marshal.AllocHGlobal(Marshal.SizeOf(accentPolicy));
            Marshal.StructureToPtr(accentPolicy, accentPtr, false);
            WindowCompositionAttributeData data = new WindowCompositionAttributeData();
            data.Attribute = WindowCompositionAttribute.WCA_ACCENT_POLICY;
            data.SizeOfData = Marshal.SizeOf(accentPolicy);
            data.Data = accentPtr;

            IntPtr taskbar = FindWindow("Shell_TrayWnd", null);
            IntPtr secondTaskbar = FindWindow("Shell_SecondaryTrayWnd", null);

            SetWindowCompositionAttribute(taskbar, ref data);
            SetWindowCompositionAttribute(secondTaskbar, ref data);
        }
    }
}

Turns the Windows 10 Taskbar transparent.