DrawingCursor

// Usage:
// BrushCursor brushCursor = null;
// [...]
// brushCursor = new BrushCursor();
// someControl.Cursor = brushCursor.CreateCursor(Color.Red, 10);
// [...]
// someControl.Cursor = brushCursor.CreateCursor(Color.Blue, 3);
// [...]
// brushCursor.Dispose();
// someControl.Cursor = Cursors.Default;

    using System;
    using System.Drawing;
    using System.Drawing.Drawing2D;
    using System.Runtime.InteropServices;
    using System.Windows.Forms;

    public class BrushCursor : IDisposable
    {
        private Cursor currentCursor = null;

        public Cursor CreateCursor(Color color, int size)
        {
            if (currentCursor != null) Dispose();
            size += (size ^ 2) == 0 ? 0 : 1;
            size = Math.Max(Math.Min(size, 16), 2);
            currentCursor = CreateCursorInternal(CreateBitmap(color, size), new Point(16, 16));
            return currentCursor;
        }

        private static Cursor CreateCursorInternal(Bitmap bitmap, Point hotSpot)
        {
            var iconInfo = new ICONINFO(hotSpot, bitmap.GetHbitmap());

            IntPtr memPtr = Marshal.AllocHGlobal(Marshal.SizeOf(iconInfo));
            Marshal.StructureToPtr(iconInfo, memPtr, true);
            IntPtr curPtr = CreateIconIndirect(memPtr);

            DestroyIcon(memPtr);
            DeleteObject(iconInfo.hbmMask);
            DeleteObject(iconInfo.hbmColor);

            return new Cursor(curPtr);
        }

        private Bitmap CreateBitmap(Color color, int size)
        {
            var bitmap = new Bitmap(32, 32);
            var rect = new RectangleF(Point.Empty, bitmap.Size);

            using (var g = Graphics.FromImage(bitmap))
            using (var brush = new SolidBrush(color))
            using (var pen = new Pen(Color.FromArgb(48, 48, 48)) { DashStyle = DashStyle.Dot }) {

                // Clip the central region to support a transparent color
                g.SetClip(RectangleF.Inflate(rect, -8, -8), CombineMode.Exclude);
                g.DrawLine(pen, rect.Width / 2f, 0, rect.Width / 2f, rect.Height);
                g.DrawLine(pen, 0, rect.Height / 2f, rect.Width, rect.Height / 2f);
                g.ResetClip();

                var spot = new RectangleF(new PointF((32 - size) / 2, (32 - size) / 2), new SizeF(size, size));
                g.SmoothingMode = SmoothingMode.AntiAlias;
                g.FillEllipse(brush, spot);
            }
            return bitmap;
        }

        public void Dispose() {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        protected virtual void Dispose(bool disposing) {
            currentCursor?.Dispose();
            currentCursor = null;
        }

        private struct ICONINFO {
            public bool fIcon;
            public int xHotspot;
            public int yHotspot;
            public IntPtr hbmMask;
            public IntPtr hbmColor;

            public ICONINFO(Point hotSpot, IntPtr hBitmap) {
                fIcon = false;
                xHotspot = hotSpot.X;
                yHotspot = hotSpot.Y;
                hbmMask = hBitmap;
                hbmColor = hBitmap;
            }
        }

        [DllImport("user32.dll", SetLastError = true)]
        private static extern IntPtr CreateIconIndirect(IntPtr iconInfo);

        [DllImport("user32.dll", SetLastError = true)]
        private static extern bool DestroyIcon(IntPtr hIcon);

        [DllImport("gdi32.dll")]
        private static extern bool DeleteObject(IntPtr hObject);
    }